Highly pumped absorption and high reliability active optical fiber

Abstract

The application provides an active optical fiber with high pump absorption and high reliability, which comprises, in sequence from inside to outside in the radial direction, a fiber core, an inner cladding, a fluorine-doped buffer layer, an outer cladding and a protective layer, wherein one or more recesses are arranged on the outer wall of the inner cladding, the recesses form a closed filling area with the inner wall of the fluorine-doped buffer layer, and the refractive index of the closed filling area is smaller than that of the inner cladding and larger than that of the fluorine-doped buffer layer. By arranging the closed filling area and the fluorine-doped buffer layer, the pump absorption coefficient can be improved without increasing the geometric size of the active optical fiber, and the failure risk of the outer cladding can be reduced.

Description

Technical Field

[0001] This invention relates to the field of optical fiber technology, and in particular to an active optical fiber with high pump absorption and high reliability. Background Technology

[0002] In 1988, Sintzer et al. of Polaroid Corporation in the United States proposed double-clad fiber and cladding pumping technology, which greatly improved the conversion efficiency of pump light in optical fibers, representing a major breakthrough in the development of fiber laser technology. Double-clad active optical fibers generally consist of a core, inner cladding, outer cladding, and a protective layer. Rare-earth ions, such as Yb, are doped into the core. 3+ Er 3+ Tm 3+ Ho 3+ When the pump light enters the fiber core, the rare-earth ions are excited, thus generating laser output at the corresponding wavelength. Since the refractive indices of the inner and outer cladding layers are much higher than those of the fiber core and inner cladding layer, the fiber core and inner cladding layer form a dual-light-guiding structure. The fiber core layer can serve as a dielectric gain laser, while the inner cladding layer can transmit the pump light.

[0003] To improve pump efficiency, double-clad ytterbium-doped fibers typically employ a non-circular inner cladding structure, such as a D-shape, square, or octagonal structure. This breaks the spiral beam, allowing more pump light to enter the fiber core and increasing the fiber laser's output power. However, as the output power of fiber lasers continues to increase, the risk of failure in the outer cladding of the pump waveguide structure also increases.

[0004] Currently, double-clad active optical fibers generally employ an octagonal inner cladding structure, with an outer cladding coated using low-refractive-index acrylic resin, such as... Figure 1 As shown. In order to meet the increasing high power demand of fiber lasers, the current main method is to increase the output power of fiber lasers by increasing the geometry of active optical fibers. However, this method has the following shortcomings: (1) The operation process and equipment for fiber drawing and testing are more demanding, and the equipment replacement cost is high; (2) The increase in fiber size will cause more fiber preform loss during the drawing process, resulting in a lower fiber drawing pass rate; (3) Although the increase in fiber size increases the output power of fiber lasers, the outer cladding material is still low-refractive-index acrylic resin, and acrylic resin has poor heat resistance, which increases the risk of outer cladding failure; (4) The inner cladding of conventional passive optical fibers is a circular structure, which has poor matching with the active optical fiber with an octagonal inner cladding structure, which will increase fiber loss and reduce beam quality; (5) The increase in the geometry of active optical fibers requires the matching geometry of passive optical fibers to be increased simultaneously, which also has the shortcomings mentioned above (1), (2), and (4). Summary of the Invention

[0005] The application provides a kind of active optical fiber of high pump absorption and high reliability, to solve the defects of low pump absorption coefficient and increased failure risk of outer cladding in prior art, increase pump absorption coefficient and reduce the failure risk of outer cladding without increasing the geometric size of active double-clad optical fiber.

[0006] The application provides a kind of active optical fiber of high pump absorption and high reliability, which comprises, in order from inside to outside along the radial direction: a core, an inner cladding, a fluorine-doped buffer layer, an outer cladding, and a protective layer.

[0007] According to the application, the shape of the enclosed filling area can be any shape.

[0008] According to the application, the depth and width of the enclosed filling area are both less than 2 / 3 of the radius of the circular structure of the inner cladding.

[0009] According to the application, when there are multiple enclosed filling areas, they can have the same or different shapes, and can be evenly or unevenly distributed along the outer wall of the inner cladding.

[0010] According to the application, the enclosed filling area is low-refractive-index glass, preferably with a numerical aperture of 0-0.2 relative to silica glass.

[0011] According to the application, the inner cladding is silica glass.

[0012] According to the application, the fluorine-doped buffer layer is fluorine-doped silica glass, and its outer wall is circular, preferably with a numerical aperture of 0.15-0.35 relative to silica glass.

[0013] According to the application, the inner wall of the fluorine-doped buffer layer is also provided with recesses, which together with the recesses provided on the outer wall of the inner cladding form the enclosed filling area.

[0014] The active optical fiber with high pump absorption and high reliability provided by the application has a core of doped silica glass, wherein the doping elements are at least one of F, B, P, Ge, Al, Yb, Tm, Er and Ho, the refractive index of the core is greater than the refractive index of the inner cladding, and the numerical aperture relative to the silica glass is preferably between 0.01 and 0.3.

[0015] The active optical fiber with high pump absorption and high reliability provided by the application has an outer cladding with a refractive index less than the refractive index of the fluorine-doped buffer layer, and the numerical aperture relative to the silica glass is greater than or equal to 0.3.

[0016] The active optical fiber with high pump absorption and high reliability provided by the application is of a full solid design, and no air layer or air area exists.

[0017] The active optical fiber with high pump absorption and high reliability provided by the application has a closed filling area arranged at the edge of the inner cladding, the waveguide area of the inner cladding is reduced, the transmission efficiency of the cladding pump light is improved, the cladding pump absorption coefficient of the active optical fiber is greatly improved, the closed filling area is arranged to make the inner cladding into a non-circular structure, thereby breaking the spiral light and allowing more pump light to enter the core and improving the optical fiber laser output power, the fluorine-doped buffer layer is arranged, and the refractive index relationship of the layers is inner cladding>closed filling area>fluorine-doped buffer layer>outer cladding, so that a large amount of cladding light is totally reflected at the interface between the fluorine-doped buffer layer and the inner cladding, only a small amount of cladding light is totally reflected at the interface between the fluorine-doped buffer layer and the outer cladding, the failure risk of the outer cladding in the light guiding process is reduced, and the optical fiber reliability is improved. BRIEF DESCRIPTION OF DRAWINGS

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

[0019] Figure 1 is a structural schematic diagram of a conventional double-clad active optical fiber in the prior art;

[0020] Figure 2 is one of the structural schematic diagrams of the active optical fiber provided by the application;

[0021] Figure 3 is the second structural schematic diagram of the active optical fiber provided by the application;

[0022] Figure 4 is the third structural schematic diagram of the active optical fiber provided by the application;

[0023] Figure 5 Fig. 4 is a structural schematic diagram of an active optical fiber provided by the present application;

[0024] Figure 6 Fig. 5 is a structural schematic diagram of an active optical fiber provided by the present application;

[0025] Figure 7 Fig. 6 is a structural schematic diagram of an active optical fiber provided by the present application;

[0026] Figure 8 Fig. 7 is a structural schematic diagram of an active optical fiber provided by the present application.

[0027] Reference signs:

[0028] 101, 201, 301, 401: fiber core; 102, 202, 302, 402: inner cladding; 103, 203, 303, 403: closed filling area; 104, 204, 304, 404: fluorine-doped buffer layer; 105, 205, 305, 405: outer cladding; 106, 206, 306, 406: protective layer. DETAILED DESCRIPTION

[0029] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be described clearly and completely below with reference to the drawings in the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0030] The present application provides a high-pump-absorption and high-reliability active optical fiber. Figures 2 to 8 The present application provides a high-pump-absorption and high-reliability active optical fiber.

[0031] The present application provides a high-pump-absorption and high-reliability active optical fiber, a structural schematic diagram of which is shown in Fig. 1, which comprises, in sequence from inside to outside along the radial direction: a fiber core 101, an inner cladding 102, a fluorine-doped buffer layer 104, an outer cladding 105 and a protective layer 106. Figure 2 The present application provides a high-pump-absorption and high-reliability active optical fiber, a structural schematic diagram of which is shown in Fig. 1, which comprises, in sequence from inside to outside along the radial direction: a fiber core 101, an inner cladding 102, a fluorine-doped buffer layer 104, an outer cladding 105 and a protective layer 106.

[0032] The embodiment of the present application reduces the effective light guide area in the inner cladding 102 by arranging the closed filling area 103 with a smaller refractive index than the inner cladding 102, thereby improving the transmission efficiency of the cladding pumped light. In addition, the filling area can increase the disturbance to make the light at the outer edge pass through the fiber core as soon as possible and be absorbed by the fiber core, thereby greatly improving the cladding pumping absorption coefficient of the active optical fiber, and further improving the output power of the fiber laser. At the same time, the inner cladding 102 becomes a non-circular structure due to the arrangement of the closed filling area 103, thereby breaking the spiral light and allowing more pump light to enter the fiber core, thereby improving the output power of the fiber laser. When the pump light is transmitted in the conventional circular double-cladding active optical fiber, most of the light is transmitted in the form of spiral light, the spiral light does not pass through the fiber core, which causes the fiber core to be unable to absorb the part of the light, thereby reducing the pump absorption efficiency.

[0033] In addition, the present application arranges the fluorine-doped buffer layer 104, and the refractive index relationship of each layer is inner cladding 102>closed filling area 103>fluorine-doped buffer layer 104>outer cladding 105, so that a large amount of cladding light is totally reflected at the interface between the fluorine-doped buffer layer 104 and the inner cladding 102, resulting in only a small amount of cladding light being totally reflected at the interface between the fluorine-doped buffer layer 104 and the outer cladding 105, thereby reducing the pressure on the outer cladding 105 to bear the cladding light and improving the reliability of the optical fiber. The proportion of the cladding light totally reflected at the interface between the inner cladding 102 and the fluorine-doped buffer layer 104 and totally reflected at the interface between the fluorine-doped buffer layer 104 and the outer cladding 105 is mainly determined by the refractive index between each layer.

[0034] In summary, the present application arranges the closed filling area 103 and the fluorine-doped buffer layer 104 to improve the pump absorption coefficient of the active optical fiber without changing the geometric size of the active optical fiber, reduce the risk of failure of the outer cladding in the light guide process, and reduce the cost of equipment update and the additional loss of materials in the manufacturing process.

[0035] The fiber core 101 is doped silica glass, wherein the doping elements are at least one of F, B, P, Ge, Al, Yb, and Tm, for example, the doping elements are Yb, or the doping elements are Yb and Tm. When the doping elements are more than two, they can be combined in any ratio.

[0036] The refractive index of the fiber core 101 is greater than the refractive index of the inner cladding 102, and preferably, the numerical aperture relative to the silica glass is between 0.01 and 0.3.

[0037] The inner cladding 102 is silica glass wrapped outside the fiber core 101. It should be noted that the silica glass is silica glass without any other doping elements, and the purity meets the actual demand.

[0038] The shape of the closed filling area 103 can be any shape, regular or irregular. Specifically, it can be U-shaped (as shown in FIG. 1), rectangular (as shown in FIG. 2), or fan-shaped (as shown in FIG. 3). Figure 2 , Figure 3 Figure 4 , Figure 5 Figure 6 , Figure 7

[0039] The depth and width of the closed filling area 103 are both less than 2 / 3 of the radius of the circular structure of the inner cladding layer 102. It should be noted that the depth refers to the distance between the point of the closed filling area 103 closest to the center and the point farthest from the center, i.e., the maximum depth of the recess. The width refers to the widest distance of the closed filling area 103 along the circumferential direction of the inner cladding layer 102.

[0040] Since the recess can be one or more, the closed filling area 103 can be one or more. For example, Figure 2 in the U-shaped closed filling area 103, there are two, Figure 3 in the U-shaped closed filling area 103, there are five, Figure 4 in the rectangular closed filling area 203, there are four, Figure 5 in the rectangular closed filling area 203, there are three, Figure 6 in the fan-shaped closed filling area 303, there are four, Figure 7 in the fan-shaped closed filling area 303, there are six.

[0041] When there are multiple closed filling areas 103, they can be the same or different in shape, and they can be evenly or unevenly distributed along the outer wall of the inner cladding layer 102. Preferably, when there are multiple closed filling areas 103, they are the same in shape and size and are evenly distributed along the outer wall of the inner cladding layer 102, as shown in FIGS. 1, 2, and 3. Figure 2 Figure 3

[0042] Specifically, the closed filling area 103 is a low-refractive-index glass with a refractive index less than that of the inner cladding layer 102, which can be fluorine-doped silica glass. The preferred numerical aperture of the closed filling area 103 relative to silica glass is between 0 and 0.2.

[0043] The fluorine-doped buffer layer 104 is fluorine-doped silica glass, and its outer wall is circular. The preferred numerical aperture relative to silica glass is between 0.15 and 0.35. It should be noted that although both the closed filling area 103 and the fluorine-doped buffer layer 104 can be fluorine-doped silica glass, the fluorine concentration of the two is different.

[0044] In the present application, since the fluorine-doped buffer layer 104 is a circular structure, it is size-matched with the passive optical fiber of a circular structure when fusion splicing, thereby improving the fusion splicing accuracy and reducing the fusion splicing loss.​​​​​

[0045] In some embodiments of the present application, the inner wall of the fluorine-doped buffer layer 404 is also provided with a recess, which cooperates with the recess provided on the outer wall of the inner cladding layer 402 to form the closed filling area 403. As shown in the figure, the closed filling area 403 is partly in the circular area of the inner cladding layer 402 and partly in the circular area of the fluorine-doped buffer layer 404. Figure 8

[0046] The outer cladding layer 105 is generally a low-refractive fluorine-containing acrylic resin coating layer, which has a refractive index smaller than that of the fluorine-doped buffer layer 104, and preferably has a numerical aperture relative to silica glass greater than or equal to 0.3, and more preferably greater than or equal to 0.46.

[0047] That is, the active optical fiber provided by the embodiments of the present application has a structure with a refractive index from high to low as follows: fiber core 101 > inner cladding layer 102 > closed filling area 103 > fluorine-doped buffer layer 104 > outer cladding layer 105. Such a design is conducive to reducing the total reflection of cladding light at the interface between the fluorine-doped buffer layer 104 and the outer cladding layer 105, so that a large amount of cladding light is totally reflected at the interface between the fluorine-doped buffer layer 104 and the inner cladding layer 102, thereby reducing the pressure on the outer cladding layer 105 to bear the cladding light and improving the reliability of the optical fiber.

[0048] The protective layer 106 mainly plays a protective role and can use the protective layer materials commonly used in the art.

[0049] The active optical fiber provided by the embodiments of the present application has a full-solid design without air layer or air area. The problem that the double-cladding active optical fiber with air cladding is difficult to cut, fuse and match with existing optical devices due to the existence of air holes is solved.

[0050] The active optical fiber provided by the embodiments of the present application can be prepared by using the preparation means known in the art.

[0051] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for some technical features thereof; and such modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.​

Claims

1. An active optical fiber with high pump absorption and high reliability, characterized in that, The structure comprises, from the inside out, a fiber core, an inner cladding, a fluorine-doped buffer layer, an outer cladding, and a protective layer. One or more recesses are provided on the outer wall of the inner cladding, and a recess is also provided on the inner wall of the fluorine-doped buffer layer. Together with the recesses on the outer wall of the inner cladding, they form a closed filling region. A portion of this closed filling region is within the circular region of the inner cladding, and a portion is within the circular region of the fluorine-doped buffer layer. The refractive index of the closed filling region is less than that of the inner cladding but greater than that of the fluorine-doped buffer layer.

2. The active optical fiber with high pump absorption and high reliability according to claim 1, characterized in that, The shape of the closed filling region can be arbitrary.

3. The active optical fiber with high pump absorption and high reliability according to claim 2, characterized in that, The depth and width of the enclosed filling area do not exceed 2 / 3 of the radius of the inner cladding circular structure.

4. The active optical fiber with high pump absorption and high reliability according to any one of claims 1-3, characterized in that, When there are multiple closed filling regions, they may have the same or different shapes, and they may be evenly or non-evenly distributed along the outer wall of the inner cladding.

5. The active optical fiber with high pump absorption and high reliability according to any one of claims 1-3, characterized in that, The inner cladding is made of silica glass; the closed filling region is made of low-refractive-index glass, and the numerical aperture of the closed filling region relative to the silica glass is between 0 and 0.

2.

6. The active optical fiber with high pump absorption and high reliability according to claim 5, characterized in that, The fluorine-doped buffer layer is made of fluorine-doped silica glass, and its outer wall is circular.

7. The active optical fiber with high pump absorption and high reliability according to claim 6, characterized in that, The numerical pore size of the fluorine-doped buffer layer relative to the silica glass is between 0.15 and 0.

35.

8. The active optical fiber with high pump absorption and high reliability according to any one of claims 1-3, characterized in that, The fiber core is doped silica glass, wherein the doping element is at least one of F, B, P, Ge, Al, Yb, Tm, Er, and Ho, and the refractive index of the fiber core is greater than the refractive index of the inner cladding.

9. The active optical fiber with high pump absorption and high reliability according to claim 8, characterized in that, The numerical aperture of the fiber core relative to the silica glass is between 0.01 and 0.

3.

10. The active optical fiber with high pump absorption and high reliability according to any one of claims 1-3, characterized in that, The refractive index of the outer cladding layer is less than that of the fluorine-doped buffer layer.

11. The active optical fiber with high pump absorption and high reliability according to claim 10, characterized in that, The numerical pore size of the outer cladding layer relative to the silica glass is greater than or equal to 0.

3.

12. The active optical fiber with high pump absorption and high reliability according to any one of claims 1-3, characterized in that, The active optical fiber is a fully solid-state design with no air layer or air region present.

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