Homogenized optical fiber and preparation method thereof

Abstract

The invention relates to a homogenized optical fiber and a preparation method thereof. The homogenized optical fiber comprises a first core layer, a second core layer, a third core layer, an inner cladding layer and an outer cladding layer which are sequentially arranged from inside to outside, the center points of the first core layer and the second core layer coincide at a point A, the center points of the third core layer, the inner cladding layer and the outer cladding layer coincide at a point B, and the distance between the point A and the point B is larger than or equal to the radius of the first core layer; the first core layer is made of germanium and fluorine co-doped quartz glass; the second core layer is made of fluorine-doped quartz glass; and the third core layer is made of pure quartz glass. The optical fiber homogenizing effect can be improved.

Description

Technical Field

[0001] The present application relates to the field of optical fiber technology, and in particular to a homogenized optical fiber and a preparation method thereof. Background Art

[0002] As an advanced optoelectronic technology, fiber laser technology has shown great potential and value in many industrial fields. In actual use, fiber lasers often suffer damage at the center of the fiber end face at the injection end. This is mainly because the power density at the center of the injection spot is very high, which will cause a significant increase in damage to its central radiation area. The fiber homogenization technology can effectively reduce the probability of fiber end face damage.

[0003] There are three main types of homogenized fiber structures at present:

[0004] The first type is to process the circular optical fiber core layer into a polygon to achieve a mode scrambling effect, such as a square homogenized optical fiber. This type of optical fiber has a certain light spot homogenization effect, but its preparation process is relatively complicated and there is a risk of bubbles being trapped in the special-shaped sleeve rod.

[0005] The second type is ordinary circular homogenized optical fiber, which is relatively simple to manufacture and can be completed in one rod making. Homogenization is mainly achieved by changing the refractive index of the core layer by doping germanium or fluorine, but the control process of the gradient refractive index is extremely high, and the change of the refractive index in the core area of ​​the symmetrical structure is not good for the homogenization effect.

[0006] The third type is asymmetric homogenized optical fiber, which mainly sets a circular satellite core around the light-guiding core layer to excite more high-order modes, and the coupling between the fundamental mode and the high-order mode realizes the homogenization effect of the Gaussian beam. However, this type of optical fiber mostly uses drilling technology to introduce the satellite core, which is relatively complicated, and the satellite core is a pure fluorine layer. The numerical aperture (NA) is limited by the limitation of the fluorine doping depth preparation process, and a higher NA cannot be achieved, and the homogenization effect is general.

[0007] Therefore, it is necessary to design a homogenized optical fiber that can achieve high beam quality homogenized beam output and has a simple preparation method. Summary of the invention

[0008] The embodiments of the present application provide a homogenized optical fiber and a preparation method thereof to improve the effect of homogenizing the optical fiber.

[0009] In a first aspect, a homogenized optical fiber is provided, which comprises a first core layer, a second core layer, a third core layer, an inner cladding layer and an outer cladding layer arranged in sequence from inside to outside;

[0010] The center points of the first core layer and the second core layer coincide with point A, the center points of the third core layer, the inner cladding layer and the outer cladding layer coincide with point B, and the distance between point A and point B is greater than or equal to the radius of the first core layer;

[0011] The material of the first core layer is germanium-fluorine co-doped quartz glass;

[0012] The material of the second core layer is fluorine-doped quartz glass;

[0013] The third core layer is made of pure quartz glass.

[0014] In some embodiments, the distance between point A and point B is equal to the radius r1 of the first core layer.

[0015] In some embodiments, the inner cladding layer is made of fluorine-doped quartz glass, and the absolute value of the relative refractive index difference Δ4 thereof is greater than the absolute value of the relative refractive index difference Δ2 of the second core layer;

[0016] The outer cladding layer is made of pure quartz glass.

[0017] In some embodiments, the relative refractive index difference Δ1 of the first core layer is 0.2% to 0.4%, wherein the relative refractive index difference contribution of fluorine is -0.05% to -0.1%;

[0018] The relative refractive index difference Δ2 of the second core layer is between -0.5% and -0.2%.

[0019] In some embodiments, the relative refractive index difference Δ4 of the inner cladding is -1.1% to -0.3%.

[0020] In some embodiments, the radius of the first core layer is r1, the radius of the second core layer is r2, and the radius of the third core layer is r3;

[0021]

[0022] In some embodiments, the diameter D1 of the first core layer is 5.0-50.0 μm, the diameter D2 of the second core layer is 6-55 μm, the diameter D3 of the third core layer is 10.0-110.0 μm, the diameter D4 of the inner cladding is 60.0-130.0 μm, and the diameter D5 of the outer cladding is 100-500 μm.

[0023] In some embodiments, the outer cladding is further provided with a coating.

[0024] In some embodiments, the refractive index of the coating is 1.370-1.420.

[0025] In a second aspect, a method for preparing a homogenized optical fiber is provided, comprising:

[0026] A homogenized core rod is prepared by a PCVD process, wherein the homogenized core rod comprises a first core layer, a second core layer, and a portion of a third core layer;

[0027] The homogenized core rod is placed in a pure quartz sleeve and melted into a solid rod to obtain an initial homogenized mother rod;

[0028] Selecting a point in the initial homogenizing master bar as point B, and processing the initial homogenizing master bar to obtain a regular quadrilateral homogenizing master bar with point B as the center point;

[0029] Using the inscribed circle of the regular quadrilateral homogenizing master rod as the grinding boundary to perform external rounding treatment, a circular homogenizing master rod including a first core layer, a second core layer and a third core layer is obtained;

[0030] The cladding tube is prepared by using a PCVD process, wherein the cladding tube comprises an inner cladding layer and an outer cladding layer;

[0031] placing the circular homogenized mother rod in a cladding tube and melting it into a homogenized preform rod;

[0032] The homogenized preform is drawn into a homogenized optical fiber.

[0033] The beneficial effects of the technical solution provided by this application include:

[0034] The homogenized optical fiber provided in the present application introduces a double satellite core layer, namely a first core layer and a second core layer arranged concentrically, thereby making the core layer include a three-core layer structure of a double satellite core layer and a third core layer. Since the center points of the double satellite core layer and the third core layer do not coincide with each other, the asymmetrically arranged germanium-fluorine co-doped satellite core layer and the fluorine-doped satellite core layer can play an excellent light spot mode disturbance property, and can effectively disperse the energy at the center of the third core layer of pure quartz to the periphery, thereby achieving a better effect of homogenizing the light spot. Therefore, it can solve the problem in the related art that the optical fiber cannot withstand higher energy due to the concentration of the light beam energy in the middle of the fiber core, and the degree of light spot homogenization is low, and finally achieve the mode disturbance effect on the laser output.

[0035] Homogenized optical fiber achieves the homogenization effect on Gaussian beams by exciting more high-order modes and coupling between fundamental mode and high-order modes. However, the existing satellite core of homogenized optical fiber adopts a pure silicon core plus fluorine-doped design, and the numerical aperture NA is limited by the limitation of the fluorine-doped depth preparation process, and a higher NA cannot be achieved. The homogenized optical fiber provided in this application adopts a three-core layer structure, and the satellite core adopts a germanium-doped and fluorine-doped design, which can increase the numerical aperture and the number of modes in the optical fiber, thereby enhancing the coupling effect between modes and improving the homogenization effect of the optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0037] Figure 1 A cross-sectional view of a homogenized optical fiber provided in an embodiment of the present application;

[0038] Figure 2 A schematic diagram of a homogenized optical fiber provided in an embodiment of the present application;

[0039] Figure 3 A homogenized optical fiber refractive index distribution diagram provided in an embodiment of the present application;

[0040] Figure 4 A flow chart for preparing a homogenized optical fiber according to an embodiment of the present application.

[0041] In the figure: 1, first core layer; 2, second core layer; 3, third core layer; 4, inner cladding; 5, outer cladding; 6, pure quartz casing. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0043] See also Figure 1 and Figure 2 As shown, an embodiment of the present application provides a homogenized optical fiber, which includes a first core layer 1, a second core layer 2, a third core layer 3, an inner cladding 4 and an outer cladding 5 arranged in sequence from the inside to the outside along the radial direction; the center points of the first core layer 1 and the second core layer 2 coincide with point A, the center points of the third core layer 3, the inner cladding 4 and the outer cladding 5 coincide with point B, and the distance between point A and point B is greater than or equal to the radius of the first core layer 1; the material of the first core layer 1 is germanium-fluorine co-doped quartz glass; the material of the second core layer 2 is fluorine-doped quartz glass; the material of the third core layer 3 is pure quartz glass.

[0044] The homogenized optical fiber provided in the present application introduces a double satellite core layer, namely a first core layer 1 and a second core layer 2 arranged concentrically, thereby making the core layer include a three-core layer structure of a double satellite core layer and a third core layer 3. Since the center points of the double satellite core layers and the third core layer 3 do not coincide, the asymmetrically arranged germanium-fluorine co-doped satellite core layer and the fluorine-doped satellite core layer can have excellent light spot mode disturbance characteristics, and can effectively disperse the energy at the center of the third core layer 3 of pure quartz to the periphery, thereby achieving a better effect of homogenizing the light spot. Therefore, it can solve the problem in the related art that the optical fiber cannot withstand higher energy due to the concentration of the light beam energy in the middle of the fiber core, and the degree of light spot homogenization is low, and finally achieve the mode disturbance effect on the laser output.

[0045] Homogenized optical fiber achieves the homogenization effect on Gaussian beams by exciting more high-order modes and coupling between fundamental mode and high-order modes. However, the existing satellite core of homogenized optical fiber adopts a pure silicon core plus fluorine-doped design, and the numerical aperture NA is limited by the limitation of the fluorine-doped depth preparation process, and a higher NA cannot be achieved. The homogenized optical fiber provided in this application adopts a three-core layer structure, and the satellite core adopts a germanium-doped and fluorine-doped design, which can increase the numerical aperture and the number of modes in the optical fiber, thereby enhancing the coupling effect between modes and improving the homogenization effect of the optical fiber.

[0046] It can be understood that the first core layer 1, the second core layer 2, the third core layer 3, the inner cladding layer 4 and the outer cladding layer 5 can independently be circular, or other shapes such as elliptical, square, etc., preferably, circular.

[0047] Furthermore, the distance between point A and point B is equal to the radius r1 of the first core layer 1, so that the outer circle of the first core layer 1 of the optical fiber described in the present application just passes through the center of the third core layer 3. Such a structural design can maximize the optical fiber homogenization effect.

[0048] Furthermore, the material of the inner cladding 4 is fluorine-doped quartz glass, and the absolute value of its relative refractive index difference Δ4 is ​​greater than the absolute value of the relative refractive index difference Δ2 of the second core layer 2. The inner cladding 4 limits light to ensure that light is transmitted in the third core layer 3, while the second core layer 2 mainly realizes mode scrambling. If the relative refractive index difference is lower than the relative refractive index difference of the inner cladding 4, it is easy to cause abnormal light transmission; the material of the outer cladding 5 is pure quartz glass.

[0049] Further, see Figure 3 As shown, the relative refractive index difference Δ1 of the first core layer 1 is 0.2% to 0.4%, of which the relative refractive index difference contribution of fluorine is -0.05% to -0.1%; the relative refractive index difference Δ2 of the second core layer 2 is -0.5% to -0.2%.

[0050] The relative refractive index difference Δ4 of the inner cladding 4 is -1.1% to -0.3%.

[0051] Relative refractive index difference:

[0052] Where n0 is the refractive index of pure quartz; i = 1, 2, 3, 4, 5, when i = 1, n i is the refractive index of the first core layer 1, when i=2, n i is the refractive index of the second core layer 2, and so on.

[0053] Further, the radius of the first core layer 1 is r1, the radius of the second core layer 2 is r2, and the radius of the third core layer 3 is r3;

[0054] r3>2r2>2r1,

[0055] Further, see Figure 3 As shown, the diameter D1 of the first core layer 1 is 5.0-50.0 μm, the diameter D2 of the second core layer 2 is 6-55 μm, the diameter D3 of the third core layer 3 is 10.0-110.0 μm, the diameter D4 of the inner cladding 4 is 60.0-130.0 μm, and the diameter D5 of the outer cladding 5 is 100-500 μm.

[0056] Furthermore, the outer cladding 5 is also provided with a coating. The refractive index of the coating is 1.370-1.420. The coating can be made of commonly used materials, such as polyacrylate.

[0057] See also Figure 4 As shown, the embodiment of the present application also provides a method for preparing a homogenized optical fiber, which comprises the following steps:

[0058] 101: A homogenized core rod is prepared by using a PCVD process, wherein the homogenized core rod includes a first core layer 1 , a second core layer 2 , and a portion of a third core layer 3 .

[0059] 102: Put the homogenized core rod into the pure quartz sleeve 6 and melt it into a solid rod to obtain an initial homogenized mother rod.

[0060] In step 102, a thinning operation may be performed according to actual needs.

[0061] 103: Mounting the initial homogenizing master rod on a precision CNC grinding machine, selecting a point in the initial homogenizing master rod as point B, and processing the initial homogenizing master rod to obtain a regular quadrilateral homogenizing master rod with point B as the center point, wherein the cross section of the regular quadrilateral homogenizing master rod is a regular quadrilateral.

[0062] It can be understood that if the distance between point A and point B is equal to the radius r1 of the first core layer 1 , then the point selected in step 103 is the tangent point on the first core layer 1 .

[0063] 104: Mount the quadrilateral homogenizing master rod on a precision CNC grinder, and perform external grinding with the inscribed circle of the quadrilateral homogenizing master rod as the grinding boundary to obtain a circular homogenizing master rod containing a first core layer 1, a second core layer 2 and a complete third core layer 3, wherein the cross section of the circular homogenizing master rod is circular.

[0064] 105 : A cladding tube is prepared by using a PCVD process, wherein the cladding tube includes an inner cladding 4 and an outer cladding 5 .

[0065] 106: placing the circular homogenized mother rod in a cladding tube and melting it into a homogenized preform rod.

[0066] 107: Drawing the homogenized preform into a homogenized optical fiber.

[0067] Among them, in step 105, if the outer cladding 5 is thick, the outer cladding 5 can be prepared in steps. Specifically: in step 105, the cladding tube includes a part of the outer cladding 5, which is melted in step 106, stretched thin, and then inserted into a pure quartz sleeve, and melted again into a solid rod, so that the pure quartz sleeve becomes a part of the outer cladding 5, thereby obtaining a complete outer cladding 5.

[0068] In this application, the homogenized core rod and cladding tube are all prepared by PCVD process, which can accurately control the profile of the homogenized core rod and the fluorine doping depth of the cladding tube, with low preparation difficulty and low attenuation. In addition, the dual satellite core in this application does not use drilling process, but uses casing combined with external grinding to reduce the difficulty of process implementation.

[0069] Embodiment 1:

[0070] The homogenized optical fiber for laser transmission comprises a circular first core layer 1, an annular second core layer 2, an annular third core layer 3, an annular inner cladding 4, and an annular outer cladding 5. In terms of geometric dimensions, the diameter D1 of the first core layer 1 is controlled to be 16μm, the diameter D2 of the second core layer 2 is controlled to be 18μm, the diameter D3 of the third core layer 3 is controlled to be 50μm, the diameter D4 of the inner cladding 4 is controlled to be 70μm, the diameter D5 of the outer cladding is controlled to be 358μm, and the distance d between point A and point B is controlled to be 8μm. In terms of refractive index, the relative refractive index difference Δ1 of the first core layer 1 is controlled to be 0.2%, the relative refractive index difference Δ2 of the second core layer 2 is controlled to be -0.3%, and the relative refractive index difference Δ4 of the inner cladding 4 is controlled to be -0.6%. The main parameters of the drawn homogenized optical fiber for laser transmission are shown in Table 1.

[0071] Table 1

[0072] characteristic condition data unit Attenuation coefficient 1080nm 1.2 dB / km The first core layer NA - 0.09 - The second core layer NA - 0.11 - Inner cladding NA - 0.16 - Transmission power 1080nm 3000 W Spot uniformity - 0.91 -

[0073] The light spot uniformity of the homogenized optical fiber is α=W1 / W2, wherein W1 is the energy in the barrel when the light intensity drops to 50% of the maximum light intensity, and W2 is the energy in the barrel when the light intensity drops to 90% of the maximum light intensity.

[0074] Embodiment 2:

[0075] The homogenized optical fiber for laser transmission comprises a circular first core layer 1, an annular second core layer 2, an annular third core layer 3, an annular inner cladding 4, and an annular outer cladding 5. In terms of geometric dimensions, the diameter D1 of the first core layer 1 is controlled to be 32μm, the diameter D2 of the second core layer 2 is controlled to be 36μm, the diameter D3 of the third core layer 3 is controlled to be 100μm, the diameter D4 of the inner cladding 4 is controlled to be 120μm, the diameter D5 of the outer cladding is controlled to be 360μm, and the distance d between point A and point B is controlled to be 16μm. In terms of refractive index, the relative refractive index difference Δ1 of the first core layer 1 is controlled to be 0.25%, the relative refractive index difference Δ2 of the second core layer 2 is controlled to be -0.35%, and the relative refractive index difference Δ4 of the inner cladding 4 is controlled to be -0.4%. The main parameters of the drawn homogenized optical fiber for laser transmission are shown in Table 2.

[0076] Table 2

[0077]

[0078]

[0079] Embodiment 3:

[0080] The homogenized optical fiber for laser transmission comprises a circular first core layer 1, an annular second core layer 2, an annular third core layer 3, an annular inner cladding 4, and an annular outer cladding 5. In terms of geometric dimensions, the diameter D1 of the first core layer 1 is controlled to be 13μm, the diameter D2 of the second core layer 2 is controlled to be 14μm, the diameter D3 of the third core layer 3 is controlled to be 40μm, the diameter D4 of the inner cladding 4 is controlled to be 75μm, the diameter D5 of the outer cladding is controlled to be 250μm, and the distance d between point A and point B is controlled to be 6.5μm. In terms of refractive index, the relative refractive index difference Δ1 of the first core layer 1 is controlled to be 0.30%, the relative refractive index difference Δ2 of the second core layer 2 is controlled to be -0.40%, and the relative refractive index difference Δ4 of the inner cladding 4 is controlled to be -0.6%. The main parameters of the drawn homogenized optical fiber for laser transmission are shown in Table 3.

[0081] Table 3

[0082] characteristic condition data unit Attenuation coefficient 1080nm 1.3 dB / km The first core layer NA - 0.11 - The second core layer NA - 0.13 - Inner cladding NA - 0.16 - Transmission power 1080nm 3000 W Spot uniformity - 0.92 -

[0083] Embodiment 4:

[0084] The homogenized optical fiber for laser transmission comprises a circular first core layer 1, an annular second core layer 2, an annular third core layer 3, an annular inner cladding 4, and an annular outer cladding 5. In terms of geometric dimensions, the diameter D1 of the first core layer 1 is controlled to be 15 μm, the diameter D2 of the second core layer 2 is controlled to be 16 μm, the diameter D3 of the third core layer 3 is controlled to be 55 μm, the diameter D4 of the inner cladding 4 is controlled to be 80 μm, the diameter D5 of the outer cladding is controlled to be 400 μm, and the distance d between point A and point B is controlled to be 7.5 μm. In terms of refractive index, the relative refractive index difference Δ1 of the first core layer 1 is controlled to be 0.35%, the relative refractive index difference Δ2 of the second core layer 2 is controlled to be -0.45%, and the relative refractive index difference Δ4 of the inner cladding 4 is controlled to be -0.9%. The main parameters of the drawn homogenized optical fiber for laser transmission are shown in Table 4.

[0085] Table 4

[0086] characteristic condition data unit Attenuation coefficient 1080nm 1.0 dB / km The first core layer NA - 0.12 - The second core layer NA - 0.14 - Inner cladding NA - 0.19 - Transmission power 1080nm 3000 W Spot uniformity - 0.93 -

[0087] Embodiment 5:

[0088] The homogenized optical fiber for laser transmission comprises a circular first core layer 1, an annular second core layer 2, an annular third core layer 3, an annular inner cladding 4, and an annular outer cladding 5. In terms of geometric dimensions, the diameter D1 of the first core layer 1 is controlled to be 25μm, the diameter D2 of the second core layer 2 is controlled to be 27μm, the diameter D3 of the third core layer 3 is controlled to be 75μm, the diameter D4 of the inner cladding 4 is controlled to be 95μm, the diameter D5 of the outer cladding is controlled to be 365μm, and the distance d between point A and point B is controlled to be 7.5μm. In terms of refractive index, the relative refractive index difference Δ1 of the first core layer 1 is controlled to be 0.4%, the relative refractive index difference Δ2 of the second core layer 2 is controlled to be -0.50%, and the relative refractive index difference Δ4 of the inner cladding 4 is controlled to be -1.1%. The main parameters of the drawn homogenized optical fiber for laser transmission are shown in Table 5.

[0089] Table 5

[0090] characteristic condition data unit Attenuation coefficient 1080nm 0.9 dB / km The first core layer NA - 0.13 - The second core layer NA - 0.15 - Inner cladding NA - 0.22 - Transmission power 1080nm 3000 W Spot uniformity - 0.91 -

[0091] Comparative Example 1:

[0092] The homogenized optical fiber for laser transmission comprises a circular second core layer 2, an annular third core layer 3, an annular inner cladding layer 4, and an annular outer cladding layer 5. In terms of geometric dimensions, the diameter D2 of the second core layer 2 is controlled to be 18 μm, the diameter D3 of the third core layer 3 is controlled to be 50 μm, the diameter D4 of the inner cladding layer 4 is controlled to be 70 μm, the diameter D5 of the outer cladding layer is controlled to be 358 μm, and the distance d between point A and point B is controlled to be 8 μm. In terms of refractive index, the relative refractive index difference Δ2 of the second core layer 2 is controlled to be -0.3%, and the relative refractive index difference Δ4 of the inner cladding layer 4 is controlled to be -0.6%. The main parameters of the drawn homogenized optical fiber for laser transmission are shown in Table 6.

[0093] Table 6

[0094] characteristic condition data unit Attenuation coefficient 1080nm 1.2 dB / km The second core layer NA - 0.11 - Inner cladding NA - 0.16 - Transmission power 1080nm 3000 W Spot uniformity - 0.85 -

[0095] In the description of the present application, it should be noted that the terms "upper", "lower", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. Unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be a connection between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0096] It should be noted that, in this application, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0097] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A homogenized optical fiber, characterized in that: It comprises a first core layer (1), a second core layer (2), a third core layer (3), an inner cladding layer (4) and an outer cladding layer (5) which are arranged in sequence from the inside to the outside; The center points of the first core layer (1) and the second core layer (2) coincide with point A, the center points of the third core layer (3), the inner cladding layer (4) and the outer cladding layer (5) coincide with point B, and the distance between point A and point B is greater than or equal to the radius of the first core layer (1); The material of the first core layer (1) is germanium-fluorine co-doped quartz glass; The material of the second core layer (2) is fluorine-doped quartz glass; The material of the third core layer (3) is pure quartz glass.

2. The homogenized optical fiber according to claim 1, characterized in that: The distance between point A and point B is equal to the radius r1 of the first core layer (1).

3. The homogenized optical fiber according to claim 1, characterized in that: The material of the inner cladding layer (4) is fluorine-doped quartz glass, and the absolute value of the relative refractive index difference Δ4 thereof is greater than the absolute value of the relative refractive index difference Δ2 of the second core layer (2); The outer cladding layer (5) is made of pure quartz glass.

4. The homogenized optical fiber according to claim 1, characterized in that: The relative refractive index difference Δ1 of the first core layer (1) is 0.2% to 0.4%, wherein the relative refractive index difference contribution of fluorine is -0.05% to -0.1%; The relative refractive index difference Δ2 of the second core layer (2) is -0.5% to -0.2%.

5. The homogenized optical fiber according to claim 1, characterized in that: The relative refractive index difference Δ4 of the inner cladding (4) is between -1.1% and -0.3%.

6. The homogenized optical fiber according to claim 1, characterized in that: The radius of the first core layer (1) is r1, the radius of the second core layer (2) is r2, and the radius of the third core layer (3) is r3; r3＞2r2＞2r1， 7. The homogenized optical fiber according to claim 1, characterized in that: The diameter D1 of the first core layer (1) is 5.0 to 50.0 μm, the diameter D2 of the second core layer (2) is 6 to 55 μm, the diameter D3 of the third core layer (3) is 10.0 to 110.0 μm, the diameter D4 of the inner cladding (4) is 60.0 to 130.0 μm, and the diameter D5 of the outer cladding (5) is 100 to 500 μm.

8. The homogenized optical fiber according to claim 1, characterized in that: The outer cladding (5) is also provided with a coating.

9. The homogenized optical fiber according to claim 8, characterized in that: The refractive index of the coating is 1.370-1.

420.

10. A method for preparing a homogenized optical fiber according to any one of claims 1 to 9, characterized in that: It includes: A homogenized core rod is prepared by using a PCVD process, wherein the homogenized core rod comprises a first core layer (1), a second core layer (2), and a portion of a third core layer (3); The homogenizing core rod is placed in a pure quartz sleeve (6) and melted into a solid rod to obtain an initial homogenizing mother rod; Selecting a point in the initial homogenizing master bar as point B, and processing the initial homogenizing master bar to obtain a regular quadrilateral homogenizing master bar with point B as the center point; Using the inscribed circle of the regular quadrilateral homogenizing master rod as the grinding boundary, an external grinding process is performed to obtain a circular homogenizing master rod containing a first core layer (1), a second core layer (2) and a third core layer (3); A cladding tube is prepared by using a PCVD process, wherein the cladding tube comprises an inner cladding layer (4) and an outer cladding layer (5); placing the circular homogenized mother rod in a cladding tube and melting it into a homogenized preform rod; The homogenized preform is drawn into a homogenized optical fiber.

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