Method for welding hollow-core optical fiber and solid optical fiber

Abstract

The invention discloses a hollow-core optical fiber and solid optical fiber welding method, which comprises the following steps: a hollow-core anti-resonance optical fiber and a large-mode-field solid optical fiber are taken, and the mode field diameter of the large-mode-field solid optical fiber is smaller than that of the hollow-core anti-resonance optical fiber; reverse tapering is carried out on the large-mode-field solid-core optical fiber, so that the mode-field diameter of the large-mode-field solid-core optical fiber is within the matching range of the hollow-core anti-resonance optical fiber; respectively and simultaneously applying tension and torsion to the large-mode-field solid-core optical fiber and the hollow-core anti-resonance optical fiber after reverse tapering, and beveling the large-mode-field solid-core optical fiber and the hollow-core anti-resonance optical fiber through a fixed cutting knife; and the beveled reverse tapering large-mode-field solid-core optical fiber and the beveled hollow-core anti-resonance optical fiber are welded in a welding mode of electric arc offset and then discharge. The hollow-core optical fiber angle welding technology is adopted in the high-power laser transmission field for the first time, a full-fiber transmission mode can be achieved in high-power laser transmission, the connection loss is low, the back reflection value is low, and the connection strength is high.

Description

Technical Field

[0001] The invention belongs to the field of optical fiber technology, and relates to a method for fusion splicing a hollow-core optical fiber and a solid optical fiber, and specifically relates to a method for fusion splicing a low-loss, low-return light, high-strength hollow-core anti-resonance optical fiber and a large-mode-field solid-core optical fiber. Background Art

[0002] Hollow-core antiresonant optical fiber provides nearly free-space propagation conditions for light waves by confining light to a low-refractive-index air core for flexible transmission. Its fiber performance, such as dispersion, nonlinearity, and damage threshold, has greatly broken through the limitations of traditional solid-core single-mode quartz optical fiber, providing a new development path for the generation and transmission of fiber lasers, fiber-optic communications, and fiber-optic sensing. In the field of high-power fiber laser transmission, traditional solid-core optical fibers will cause the transmitted laser to be distorted due to nonlinear effects and dispersion, while the transmission medium of the hollow-core optical fiber core is air, and its low nonlinearity and high damage threshold provide an effective way for high-power laser transmission, which has been the focus of research in the past few years.

[0003] At present, a series of breakthroughs have been achieved based on hollow-core antiresonant fibers, such as 3kW high-power continuous laser, 30mJ single pulse energy, 20GW peak power, and 1km long-distance transmission of kW-level power, fully demonstrating its huge application potential in the field of high-power laser transmission. In addition, in the field of mid-infrared fiber lasers, it is currently difficult for rare-earth-doped soft glass fiber lasers to achieve laser output above 3μm, and the laser power level is low. By filling the hollow-core fiber with gas and utilizing the gas-rich emission wavelength, mid-infrared laser output with a wide wavelength coverage range, high power, and high beam quality can be achieved. At present, 20W and 6.6W mid-infrared laser outputs have been reported at 3.1μm and 4.3μm, respectively.

[0004] However, in the above-mentioned application fields of fiber laser generation and transmission, the connection between the hollow-core fiber and its laser system is often achieved by free-space coupling of the laser transmission system using independent optical components such as lenses and reflectors. Although this transmission method can transmit extremely high power, the device is relatively complex, the stability is relatively poor, and it is easily disturbed by the environment. The thermal effect of the coupling lens during the transmission of high-power lasers can easily cause focus shift and thus affect the transmission efficiency, which poses a considerable obstacle to its miniaturization and integration.

[0005] Therefore, in high-power laser systems, all-fiber transmission between hollow-core fibers and solid-core fibers remains a difficult problem to be solved. Summary of the invention

[0006] In view of the fact that hollow-core anti-resonant optical fibers in the prior art are difficult to efficiently and stably connect with existing high-power laser systems, the present invention provides a method for fusion splicing low-loss, low-return light, and high-intensity hollow-core anti-resonant optical fibers with large-mode-field solid-core optical fibers. The fiber post-processing technology without transition optical fibers is adopted, and the tail fibers of high-power light sources can be directly processed, thus avoiding the accumulation of thermal effects caused by multiple fusion splicing. Secondly, the angle cutting suppresses the return light caused by Fresnel reflection, effectively reducing the risk of return light damaging the light source.

[0007] The present invention discloses a method for fusion splicing a hollow core optical fiber and a solid core optical fiber, comprising:

[0008] A hollow core anti-resonant optical fiber and a large mode field solid core optical fiber are used, wherein the mode field diameter of the large mode field solid core optical fiber is smaller than the mode field diameter of the hollow core anti-resonant optical fiber;

[0009] Reversely taper the large mode field solid core optical fiber so that the mode field diameter of the large mode field solid core optical fiber is within the matching range of the hollow core anti-resonant optical fiber;

[0010] Applying tension and torsion to the large mode field solid core optical fiber and the hollow core anti-resonance optical fiber after reverse taper at the same time, and completing the beveling of the large mode field solid core optical fiber and the hollow core anti-resonance optical fiber by a fixed cutting knife;

[0011] The arc offset and re-discharge fusion splicing method is used to fusion splice the beveled reverse tapered large mode field solid core optical fiber and the beveled hollow core anti-resonant optical fiber.

[0012] As a further improvement of the present invention, the initial mode field diameter of the large mode field solid core optical fiber is in the range of 20-35 μm, and the parameters such as the mode field diameter and taper after reverse taper are in the range of 25-52 μm.

[0013] As a further improvement of the present invention, the discharge parameter of the reverse taper is 280 bits, the length of the taper zone is set to 1.5 mm, and the advancement speed is 1 mm / s.

[0014] As a further improvement of the present invention, the initial mode field diameter of the hollow core antiresonant optical fiber is in the range of 28-50 μm.

[0015] As a further improvement of the present invention, the tension range applied to the large mode field solid core optical fiber or hollow core antiresonant optical fiber after reverse taper is 650g-1200g, and the torque range is 0-8°.

[0016] As a further improvement of the present invention, the specific welding process method and parameters of the arc offset and re-discharge welding method are: main discharge amount: -85bit, discharge time: 8000ms, center offset position: 50μm.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. The present invention uses the optical fiber reverse taper technology to match hollow-core antiresonant optical fibers within a certain range. During the taper process, the light field shape and energy are almost unchanged when transmitted in the tapered optical fiber, ensuring that the taper technology will not introduce additional losses, and ultimately achieving a fusion loss of less than 0.3dB.

[0019] 2. The present invention combines the optical fiber reverse taper technology with the angle fusion technology without introducing additional materials, achieving a light return suppression of <-30dB, while the connection loss is less than 0.45dB, expanding the feasibility of fusion technology in the field of high-power laser applications.

[0020] 3. The present invention is simple to operate, highly repeatable, adaptable to various environments, and easy to realize industrialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a flow chart of the method for fusion splicing a hollow core optical fiber and a solid core optical fiber disclosed in the present invention;

[0022] Figure 2 Large mode field solid core optical fibers of different sizes with normal appearance and almost lossless reverse tapered shape;

[0023] Figure 3 Schematic diagram of angle cutting of large mode area solid core optical fiber. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0026] like Figure 1 As shown, the present invention provides a method for fusion splicing a hollow-core optical fiber and a solid optical fiber, which adopts the hollow-core optical fiber angle fusion splicing technology for the first time in the field of high-power laser transmission, and can realize a full-fiber transmission mode in high-power laser transmission, with low connection loss, low back reflection value, and high connection strength; specifically, it includes:

[0027] Step 1, take a hollow core antiresonant fiber and a large mode field solid core fiber, wherein the mode field diameter of the large mode field solid core fiber is smaller than the mode field diameter of the hollow core antiresonant fiber; specifically, the initial mode field diameter range of the large mode field solid core fiber is 20-35 μm, and the cladding diameter range is 250-450 μm; the initial mode field diameter range of the hollow core antiresonant fiber is 28-50 μm, and the cladding diameter range is 190-230 μm.

[0028] Step 2, reverse taper the large mode field solid core optical fiber so that the mode field diameter of the large mode field solid core optical fiber is within the matching range of the hollow core antiresonant optical fiber; wherein the mode field diameter after reverse taper is 25-52 μm, and the key process parameters of reverse taper are: the discharge parameter is 280 bit, the cone zone length is set to 1.5 mm, the advancement speed is 1 mm / s, and the matching range of the mode field diameter of the large mode field solid core optical fiber after taper and the mode field diameter of the hollow core antiresonant optical fiber is 28-50 μm.

[0029] Specific:

[0030] Use a special fiber fusion splicer to perform reverse taper processing of different sizes on large mode field solid core optical fibers. The parameters of the optical fiber are set through the software, and the motor is calibrated through two large mode field solid core optical fibers with flat end faces cut to ensure that the optical fiber to be tapered is in a naturally straight and untwisted state when placed; then, click the initialize button, and place the large mode field solid core optical fiber after the motor moves to the corresponding position; finally, click the taper button and wait for the fusion splicer to perform the taper operation. After the taper is completed, take out the optical fiber for characterization. Using the control variable method, through multiple attempts and optimization of the taper parameters, we finally obtained large mode field solid core optical fibers of different sizes with normal appearance and shape and almost no loss after reverse taper, such as Figure 2 As shown in the figure, the fiber reverse taper technology changes the minimum coupling loss that can be achieved between large mode field solid core fiber and hollow core antiresonant fiber. Considering the mode field diameter of the hollow core antiresonant fiber used, the core size of the large mode field solid core fiber can be reverse tapered to a size close to the mode field diameter of the hollow core fiber as needed, thereby achieving low-loss fusion splicing of large mode field solid core fiber and hollow core fiber.

[0031] Step 3, respectively apply tension and torque to the large mode field solid core optical fiber and the hollow core antiresonant optical fiber after reverse taper, and complete the beveling of the large mode field solid core optical fiber and the hollow core antiresonant optical fiber by a fixed cutting knife; wherein the tension range applied to the large mode field solid core optical fiber or the hollow core antiresonant optical fiber after reverse taper is 650g-1200g, and the torque range is 0-8°.

[0032] Specific:

[0033] Before cutting, tensile and torsional forces are applied to both the large mode area solid core fiber and the hollow core antiresonant fiber. Figure 3As shown; when the blade scratches the optical fiber, the scratch propagates on the optical fiber in a direction perpendicular to the maximum stress caused by the combination of tension and torsion, thereby completing the bevel cut to reduce the return light.

[0034] Step 4: Using arc offset and re-discharge welding method to weld the large mode field solid core optical fiber after reverse taper and the hollow core anti-resonance optical fiber after beveling, so as to achieve high-strength access without obvious deformation of the cladding structure of the hollow core anti-resonance optical fiber;

[0035] Specific:

[0036] A special optical fiber fusion splicer is used to fuse the large mode field solid core optical fiber and the hollow core antiresonant optical fiber by adopting the arc offset and re-discharge welding method. By changing the main welding parameters such as the main discharge time, the main discharge power and the electrode offset, the low structural damage and low loss welding of the large mode field solid core optical fiber and the hollow core antiresonant optical fiber is achieved. Among them, the specific welding process method and parameters of the arc offset and re-discharge welding method are: main discharge amount: -85bit, discharge time: 8000ms, center offset position: 50μm.

[0037] The advantages of the present invention are:

[0038] The present invention achieves mode field amplification of large mode field solid core optical fiber through optical fiber reverse taper technology to reduce the loss caused by mode field mismatch, thereby ensuring low-loss connection; wherein, the additional loss caused by the optical fiber reverse taper process is less than 0.01dB. The loss of the optical fiber fusion sample made by this method is <0.3dB;

[0039] Taking into account that in high-power systems, the return light is amplified in the fiber core and easily causes damage to the laser system, the present invention adopts angle cutting technology. By cutting the end face of the solid core optical fiber at an angle, a part of the reflected light can be reflected to the cladding at a certain angle, thereby reducing more reflected light in the fiber core and returning to the light source, minimizing the Fresnel reflected light caused by the difference in the refractive index of the fiber core, increasing the return loss of the optical fiber head, and reducing the risk in the practical process; by balancing back reflection and connection loss, we ensure low back reflection light while maintaining high connection efficiency.

[0040] The present invention adopts optical fiber reverse taper technology, optical fiber angle cutting technology, and arc offset re-discharge fusion splicing technology to achieve stable and deformation-free access of hollow-core optical fiber to a high-power system, thereby expanding the practicability of hollow-core optical fiber and facilitating industrial application. At the same time, the above three types of technologies only require special optical fiber fusion splicing machines and large-core diameter cutting knives to complete, and are simple to operate, low in cost, and highly repeatable. The fusion splicing method can work for a long time in various environments and has good stability.

[0041] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for fusion splicing a hollow core optical fiber and a solid core optical fiber, characterized in that: include: A hollow core anti-resonant optical fiber and a large mode field solid core optical fiber are used, wherein the mode field diameter of the large mode field solid core optical fiber is smaller than the mode field diameter of the hollow core anti-resonant optical fiber; Reversely taper the large mode field solid core optical fiber so that the mode field diameter of the large mode field solid core optical fiber is within the matching range of the hollow core anti-resonant optical fiber; Applying tension and torsion to the large mode field solid core optical fiber and the hollow core anti-resonance optical fiber after reverse taper at the same time, and completing the beveling of the large mode field solid core optical fiber and the hollow core anti-resonance optical fiber by a fixed cutting knife; The arc offset and re-discharge fusion splicing method is used to fusion splice the beveled reverse tapered large mode field solid core optical fiber and the beveled hollow core anti-resonant optical fiber.

2. The method for fusion splicing a hollow core optical fiber and a solid core optical fiber according to claim 1, characterized in that: The initial mode field diameter of the large mode field solid core optical fiber is in the range of 20-35 μm, and the parameters such as the mode field diameter and taper after reverse taper are in the range of 25-52 μm.

3. The method for fusion splicing a hollow core optical fiber and a solid core optical fiber according to claim 2, characterized in that: The discharge parameters of the reverse taper are 280 bits, the length of the cone area is set to 1.5 mm, and the advancement speed is 1 mm / s.

4. The method for fusion splicing a hollow core optical fiber and a solid core optical fiber according to claim 2, characterized in that: The initial mode field diameter of the hollow core antiresonant optical fiber is in the range of 28-50 μm.

5. The method for fusion splicing a hollow core optical fiber and a solid core optical fiber according to claim 1, characterized in that: The tension range applied to the large mode field solid core fiber or hollow core antiresonant fiber after reverse taper is 650g-1200g, and the torque range is 0-8°.

6. The method for fusion splicing a hollow core optical fiber and a solid core optical fiber according to claim 1, characterized in that: The specific welding process method and parameters of the arc offset and re-discharge welding method are: main discharge amount: -85bit, discharge time: 8000ms, center offset position: 50μm.

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