Optical fiber integrated end cap and preparation method thereof

Abstract

The present invention belongs to the technical field of optical fiber laser devices, specifically an integrated optical fiber end cap and a preparation method thereof. The integrated optical fiber end cap provided by the present invention includes: an initial optical fiber segment, a tapered transition segment of an optical fiber reverse taper structure, and a uniform waist segment of an optical fiber reverse taper structure; an optical fiber taper machine is used to perform reverse taper processing on the optical fiber to form an optical fiber reverse taper structure with a larger core diameter and cladding diameter including a tapered transition segment and a uniform waist segment, and then the reverse taper structure is subjected to thermal core expansion processing with different parameters, and finally the uniform waist segment of the reverse taper structure is cut and the rear end face is plated with an anti-reflection film; the present invention can directly prepare a seamlessly connected end cap on an energy-transmitting optical fiber, greatly improving the integrated compatibility of the optical fiber end cap, and while reducing the optical power density of the optical fiber output surface, ensuring good laser beam quality, which can meet the application requirements of all-fiber lasers and high-energy laser transmission.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber laser devices, and in particular relates to an optical fiber integrated end cap and a preparation method thereof. Background Art

[0002] High-power fiber lasers have the advantages of compact structure, high conversion efficiency, and good beam quality, and are now widely used in industrial processing, national defense, military, material processing, and other fields. At present, fiber lasers with output powers of more than kilowatts and higher usually use optical fibers with a core diameter of only tens of microns, which makes them have a very high core energy density. When the fiber laser outputs high power, contamination of the fiber end face and any small defects will cause damage to the fiber end face, and the reflected light from the end face of the output fiber will also have a serious impact on the performance of the laser.

[0003] The protection of the output end of the energy transmission fiber is the key to the safety and stable operation of the laser. At present, the fiber end cap is mainly used as the output end of the high-power fiber laser. Common fiber end cap preparation methods include: fusing a larger quartz block or glass rod at the output end of the fiber to achieve beam expansion to reduce the power density. However, due to the huge difference in the diameter of the fiber and the large-size end cap, it is difficult to achieve high-quality welding of the two; fusing multiple sections of coreless fiber at the output end of the fiber to increase the beam expansion diameter, but the effect is limited, and the laser is directly output after free transmission in the coreless fiber, which reduces the collimation performance of the fiber laser output; after fusing the quartz block or coreless fiber, an additional lens group is set at the output end of the end cap, or the output end of the end cap is precisely processed into a smooth surface using processes such as ion etching, so as to collimate the output laser while expanding the beam and improve the laser beam quality. However, this makes the preparation of the fiber end cap more complicated and cumbersome. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide an optical fiber integrated end cap with a simple structure, high integration and good output laser beam quality and a preparation method thereof.

[0005] The optical fiber integrated end cap provided by the present invention comprises an initial optical fiber segment, a tapered transition segment of an optical fiber reverse taper structure, and a uniform waist segment of an optical fiber reverse taper structure; an optical fiber reverse taper machine is used to perform reverse taper processing on the optical fiber to form an optical fiber reverse taper structure having a larger core diameter and cladding diameter and comprising a tapered transition segment and a uniform waist segment; the reverse taper structure is then subjected to thermal core expansion processing with different parameters; and finally, an anti-reflection film is plated on the rear end face of the uniform waist segment of the reverse taper structure after cutting.

[0006] The initial optical fiber may be a doped active optical fiber or a non-doped energy transmission optical fiber.

[0007] The initial optical fiber may be a single-clad optical fiber, a double-clad optical fiber, or a multi-clad optical fiber with three or more layers.

[0008] Wherein, the initial optical fiber has a core diameter of 10 μm-200 μm and a cladding diameter of 130 μm-500 μm.

[0009] The optical fiber reverse taper processing ratio is 1.1-4; the optical fiber reverse taper processing ratio is defined as the cladding diameter ratio of the uniform waist section of the optical fiber reverse taper structure to the initial optical fiber section.

[0010] After the optical fiber is subjected to reverse taper processing, the reverse taper structure is further subjected to thermal core expansion processing to obtain a larger core diameter without changing the diameter of the reverse taper structure, thereby increasing the light beam exit area.

[0011] Wherein, the optical fiber core diameter and cladding diameter of the tapered transition section of the optical fiber reverse taper structure increase monotonically as approaching the waist region of the reverse taper structure.

[0012] Wherein, an anti-reflection film is plated on the end surface of the uniform waist section of the optical fiber reverse taper structure.

[0013] The present invention also provides a method for preparing the above-mentioned integrated optical fiber end cap, the specific steps of which are:

[0014] (1) Obtain the initial energy transmission optical fiber, strip off a section of the optical fiber coating, and treat the optical fiber surface with high-purity alcohol or acetone;

[0015] (2) using an optical fiber taper machine to perform reverse taper processing on the bare fiber area obtained in step (1) to obtain an optical fiber reverse taper structure including a tapered transition section and a uniform waist section;

[0016] (3) performing thermal core expansion treatment on the optical fiber reverse taper structure;

[0017] (4) Cutting the waist section of the optical fiber reverse taper structure and coating an anti-reflection film on the end surface of the cut waist section.

[0018] The optical fiber reverse taper processing ratio is 1.1-4, and the optical fiber core diameter and cladding diameter of the tapered transition section of the optical fiber reverse taper structure increase monotonically as approaching the waist region of the reverse taper structure.

[0019] The present invention directly prepares a seamlessly connected end cap on the energy transmission optical fiber, which greatly improves the integration compatibility of the optical fiber end cap and ensures good laser beam quality while reducing the optical power density of the optical fiber output surface, and can meet the application requirements of all-fiber lasers and high-energy laser transmission.

[0020] Compared with the prior art, the present invention adopts an optical fiber taper machine to directly perform reverse taper processing on the energy transmission optical fiber, forming a beam expansion structure including a tapered transition section and a uniform waist section, and further performs thermal core expansion to expand the output beam area and reduce the output end face beam power density; in addition, compared with commonly used quartz or coreless optical fiber end caps, since these structures do not have refractive index difference restrictions, the light beam propagates freely in them, and the optical fiber integrated end cap provided by the present invention utilizes the tapered transition structure of the optical fiber and the refractive index difference restriction between the optical fiber core and the cladding, so that the beam expansion can maintain good beam quality.

[0021] The method for preparing the optical fiber integrated end cap of the present invention has a simple process and low preparation cost, and is conducive to forming a practical product. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the structure of an integrated optical fiber end cap in an embodiment of the present invention.

[0023] Figure 2 1 and 10 are the input light field (a) and output light field (b) of the optical fiber integrated end cap in the embodiment of the present invention.

[0024] Figure 3 This is the optical power density curve after energy normalization of the input and output ends of the optical fiber integrated end cap in the embodiment of the present invention.

[0025] Figure 4 The present invention is a flowchart of a method for preparing an integrated optical fiber end cap according to an embodiment of the present invention.

[0026] The numbers in the figure are: 1 is the integrated optical fiber end cap; 11 is the initial optical fiber segment; 12 is the tapered transition segment of the optical fiber reverse taper structure; 13 is the uniform waist segment of the optical fiber reverse taper structure; 111 is the core of the initial optical fiber segment; 112 is the input end face of the integrated optical fiber end cap; 121 is the core of the tapered transition segment of the optical fiber; 131 is the core of the uniform waist segment of the optical fiber; 132 is the output end face of the integrated optical fiber end cap. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0028] like Figure 1 The structure diagram of an integrated optical fiber end cap 1 in an embodiment of the present invention is shown. The integrated optical fiber end cap 1 comprises: an initial optical fiber segment 11, an optical fiber reverse taper structure tapered transition segment 12, and an optical fiber reverse taper structure uniform waist segment 13. Among them, the input end cap of the integrated end cap 1 is 112, the output end face is 132, the initial optical fiber segment core is 111, the optical fiber tapered transition segment core is 121, and the optical fiber uniform waist segment core is 131.

[0029] Specifically, the optical fiber integrated end cap 1 can be used to perform reverse taper processing on the optical fiber by using an optical fiber taper machine to form an optical fiber reverse taper structure with a larger core diameter and cladding diameter including a tapered transition section 12 and a uniform waist section 13, and then the reverse taper structure is subjected to thermal core expansion processing with different parameters, and finally cut from the uniform waist section of the reverse taper structure. The end face 132 of the output end of the optical fiber integrated end cap is coated with an anti-reflection film.

[0030] Wherein, the optical fiber core diameter and cladding diameter of the tapered transition section of the optical fiber reverse taper structure increase monotonically as approaching the waist region of the reverse taper structure.

[0031] In this embodiment, the initial optical fiber 11 is a passive 20 / 400 double-clad energy transmission optical fiber, the diameter of the core 111 of the initial optical fiber segment is 20 μm, and the diameter of the cladding is 400 μm.

[0032] The initial optical fiber 11 is stripped of a coating layer, and a fiber taper machine is used to perform a reverse taper process on the initial optical fiber, so that the fiber reverse taper processing ratio is 2, wherein the reverse taper processing ratio is defined as the ratio of the waist region of the reverse taper structure to the cladding diameter of the initial optical fiber. It is understandable that in order to meet the beam expansion requirements of a higher optical fiber integrated end cap, a higher reverse taper ratio process can also be performed.

[0033] Furthermore, after the initial optical fiber 11 is subjected to a reverse taper process, the reverse taper structure is subjected to a thermal core expansion process to obtain a larger core diameter without changing the diameter of the reverse taper structure, thereby increasing the light beam exit area. Figure 2 The figure shows the input light field (a) and output light field (b) of the optical fiber integrated end cap in the embodiment of the present invention. Figure 2 (a) and Figure 2 (b) It can be found that after the laser passes through the optical fiber integrated end cap 1, the end face of the integrated end cap output end still maintains a good light field shape, and the beam area is effectively increased, thereby reducing the optical power density of the output end face, and the beam expansion effect is obvious.

[0034] like Figure 3 The figure shows the optical power density curve after energy normalization of the optical fiber integrated end cap input end 112 and output end 132 in the above embodiment. Figure 3 It can be seen that the light field energy at the input end is very concentrated, and the optical power density curve is approximately a Gaussian curve distribution, while the optical power density at the output end is significantly reduced, and the central optical power density is reduced by 25 times.

[0035] The output end face 132 of the integrated optical fiber end cap is coated with an anti-reflection film.

[0036] like Figure 4 The flowchart shown is a method for preparing the optical fiber integrated end cap in the above embodiment, comprising the following steps:

[0037] (1) Obtain the initial energy transmission optical fiber, strip off a section of the optical fiber coating, and treat the optical fiber surface with high-purity alcohol or acetone;

[0038] (2) using an optical fiber taper machine to perform reverse taper processing on the bare fiber area obtained in step (1) to obtain an optical fiber reverse taper structure including a tapered transition section and a uniform waist section;

[0039] (3) performing thermal core expansion treatment on the optical fiber reverse taper structure;

[0040] (4) Cutting the waist section of the optical fiber reverse taper structure and coating an anti-reflection film on the end surface of the cut waist section.

[0041] In the embodiment of the present invention, a fiber taper machine is used to directly perform reverse taper processing on the energy transmission fiber to form a beam expansion structure including a tapered transition section and a uniform waist section, and further thermal core expansion is performed to expand the exit beam area, so that the power density of the optical fiber exit end face is greatly reduced. At the same time, due to the tapered transition structure of the optical fiber and the refractive index difference between the optical fiber core and the cladding, the prepared optical fiber integrated end cap can maintain good beam quality. The preparation method of the optical fiber integrated end cap proposed in the embodiment of the present invention has a simple process, high repeatability, and is easy to be practical.

[0042] Finally, the above description is only a preferred embodiment and is not intended to limit the protection scope of the present invention. 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. An integrated optical fiber end cap, characterized in that: include: The optical fiber integrated end cap is obtained by performing reverse taper processing on the optical fiber using an optical fiber taper machine to form an optical fiber reverse taper structure with a larger core diameter and cladding diameter including a tapered transition section and a uniform waist section, and then performing thermal core expansion processing with different parameters on the reverse taper structure, and finally coating an anti-reflection film on the rear end face of the uniform waist section of the reverse taper structure; wherein: The optical fiber reverse taper processing ratio is 1.1-4; The optical fiber reverse taper processing ratio is defined as the cladding diameter ratio of the uniform waist section of the optical fiber reverse taper structure to the initial optical fiber section; After the optical fiber is subjected to a reverse taper process, the reverse taper structure is further subjected to a thermal core expansion process to obtain a larger core diameter without changing the diameter of the reverse taper structure, thereby increasing the light beam exit area; The optical fiber core diameter and cladding diameter of the tapered transition section of the optical fiber reverse taper structure increase monotonically as they approach the waist region of the reverse taper structure; The core diameter of the initial optical fiber segment is 10 μm-200 μm, and the cladding diameter is 130 μm-500 μm; The end surface of the uniform waist section of the optical fiber reverse taper structure is plated with an anti-reflection film.

2. The optical fiber integrated end cap according to claim 1, characterized in that: The optical fiber is a doped active optical fiber or a non-doped energy transmission optical fiber.

3. The optical fiber integrated end cap according to claim 2, characterized in that: The optical fiber is a single-clad optical fiber, or a double-clad optical fiber, or a multi-clad optical fiber with three or more layers.

4. A method for preparing an integrated optical fiber end cap according to any one of claims 1 to 3, characterized in that: The specific steps are: (1) Obtain the initial energy transmission optical fiber, strip off a section of the optical fiber coating, and treat the optical fiber surface with high-purity alcohol or acetone; (2) using an optical fiber taper machine to perform reverse taper processing on the bare fiber area obtained in step (1) to obtain an optical fiber reverse taper structure including a tapered transition section and a uniform waist section; (3) performing thermal core expansion treatment on the optical fiber reverse taper structure; (4) cutting the waist section of the optical fiber reverse taper structure and coating an anti-reflection film on the end surface of the cut waist section; The optical fiber reverse taper processing ratio is 1.1-4, and the optical fiber core diameter and cladding diameter of the tapered transition section of the optical fiber reverse taper structure increase monotonically as approaching the waist region of the reverse taper structure.

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