Mode field adapter

Abstract

The utility model discloses a mode field adapter, which comprises a first optical fiber, a second optical fiber and a glass sleeve, and is characterized in that the first optical fiber comprises a first optical fiber body and a first connecting section which are connected; the second optical fiber comprises a second optical fiber body and a second connecting section which are connected; one end, deviating from the first optical fiber body, of the first connecting section is welded with one end, deviating from the second optical fiber body, of the second connecting section; the fiber core diameter and the cladding diameter of the first optical fiber body are D1 and S1 respectively, the fiber core diameter and the cladding diameter of the end, away from the first optical fiber body, of the first connecting section are D2 and S2 respectively, and the fiber core diameter and the cladding diameter of the second optical fiber body are D4 and S4 respectively. The fiber core diameter and the cladding diameter of one end, deviating from the second optical fiber body, of the second connection section are D3 and S3 respectively, S1 < S2 = S3 < S4, and D1 = D2 = D3 < D4. The optical fiber connector has the advantages of easiness in welding operation, low welding loss and good optical signal transmission.

Description

Technical Field

[0001] The present application belongs to the technical field of laser equipment, and in particular, relates to a mode field adapter. Background Art

[0002] The initial laser seed source of the fiber laser is output in single mode. In order to obtain higher power, a larger core fiber is used for amplification in the subsequent stage. Therefore, a mode field adapter (MFA) needs to be added between each amplification stage to keep the previous stage signal light in single mode after entering the subsequent stage.

[0003] Mode field adapters play an important role in laser products and optical communication systems. Their main function is to match the mode field diameters of different optical fibers, thereby achieving low-loss fusion splicing of large mode field fibers and ordinary single-mode fibers, allowing large mode field fibers to maintain base mode transmission and ensure the strength and quality of optical signals.

[0004] Mode field adapters include large mode field optical fibers and single mode optical fibers. Because the cladding diameter of large mode field optical fibers is larger than the retaining diameter of single mode optical fibers, and the mode field diameter of large mode field optical fibers is larger than the mode field diameter of single mode optical fibers, it is difficult to directly fuse the two. In the related art, the core of a section of optical fiber that is to be fused with a large mode field optical fiber and a single mode optical fiber is reversely tapered until the core diameter of the large mode field optical fiber is the same as the core diameter of the single mode optical fiber, and then the two are fused. However, when the diameter difference between the large mode field optical fiber and the single mode optical fiber is large, the tapering operation of the large mode field optical fiber is difficult. The fusion splicing operation of large mode field optical fibers and single mode optical fibers is difficult, the fusion loss is large, and the optical signal transmission is poor. Utility Model Content

[0005] The embodiment of the present application provides a mode field adapter to solve the problems of difficult fusion splicing operation, large fusion loss and poor optical signal transmission of existing large mode field optical fibers and single mode optical fibers.

[0006] The present application embodiment provides a mode field adapter, including:

[0007] A first optical fiber, comprising a first optical fiber body and a first connecting section connected to each other, wherein the first connecting section is located at one end of the first optical fiber body;

[0008] A second optical fiber comprises a connected second optical fiber body and a second connecting segment, wherein the second connecting segment is located at one end of the second optical fiber body, and an end of the first connecting segment facing away from the first optical fiber body is fused with an end of the second connecting segment facing away from the second optical fiber body;

[0009] A glass sleeve, wherein the glass sleeve is sleeved at the connection between the first optical fiber and the second optical fiber, and at least covers the first connecting section and the second connecting section;

[0010] The core diameter and the cladding diameter of the first optical fiber body are D1 and S1 respectively. The core diameter and the cladding diameter of one end of the first connection section away from the first optical fiber body are D2 and S2 respectively. The core diameter and the cladding diameter of the second optical fiber body are D4 and S4 respectively. The core diameter and the cladding diameter of one end of the second connection section away from the second optical fiber body are D3 and S3 respectively. Among them,

[0011] S1 < S2 = S3 < S4, and D1 = D2 = D3 < D4.

[0012] Optionally, S1 = 10μm, D1 = 125μm, S4 = 30μm, D4 = 250μm.

[0013] Optionally, S2 = S3 = 15μm.

[0014] Optionally, the core of the first connection section includes a first core section and a second core section. The first core section is located between the first optical fiber body and the second core section. The first core section connects the core of the first optical fiber body and the second core section. Among them,

[0015] The core diameter of the second core section is S2. Along the direction of the first connection section pointing to the second core section, the diameter of the first core section gradually increases.

[0016] Optionally, along the length direction of the first optical fiber, the length of the first connection section is L1, and 3mm ≤ L1 ≤ 3.5mm.

[0017] Optionally, the second connection section includes a first optical fiber section and a second optical fiber section. The first optical fiber section is located between the second optical fiber body and the second optical fiber section. The first optical fiber section connects the second optical fiber body and the second optical fiber section. Among them, the core diameter and the cladding diameter of the second optical fiber section are D3 and S3 respectively. Along the direction of the second optical fiber body pointing to the second optical fiber section, both the cladding diameter and the core diameter of the first optical fiber section gradually decrease.

[0018] Optionally, the length of the first optical fiber section is l1, and 2.5mm ≤ l1 ≤ 3.5mm;

[0019] and / or, the length of the second optical fiber section is l2, and 10mm ≤ l2 ≤ 13mm.

[0020] Optionally, the length of the second connection section is L2, and 12.5mm ≤ L2 ≤ 16.5mm.

[0021] Optionally, the glass sleeve is fixedly bonded to the first optical fiber and the second optical fiber.

[0022] Optionally, the second optical fiber is prepared by a forward tapering process.

[0023] The mode field adapter provided in the embodiment of the present application comprises a first optical fiber and a second optical fiber, the first optical fiber comprises a first optical fiber body and a first connecting segment, the second optical fiber comprises a second optical fiber body and a second connecting segment, the first connecting segment and the second connecting segment are located between the first optical fiber body and the second optical fiber body, an end of the first connecting segment away from the first optical fiber body is fused with an end of the second connecting segment away from the second optical fiber body, compared with the prior art in which the first optical fiber body is directly adapted only by the second connecting segment, the core diameter and cladding diameter of the first connecting segment in the present application correspond to the core diameter and cladding diameter of the second connecting segment, which is conducive to the fusion of the first connecting segment and the second connecting segment, the difference in core diameter between the first connecting segment and the first optical fiber body is small, and the difference in core diameter between the second connecting segment and the second optical fiber body is small, which has the advantages of easy fusion operation, small fusion loss and good optical signal transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can obtain other drawings based on these drawings without creative work.

[0025] In order to more completely understand the present application and its beneficial effects, the following description will be made in conjunction with the accompanying drawings. In the following description, the same reference numerals represent the same parts.

[0026] Figure 1 This is a labeled diagram of the mode field adapter provided in an embodiment of the present application.

[0027] Figure 2 A schematic diagram of a mode field adapter provided in an embodiment of the present application.

[0028] Figure 3 A flow chart of a method for preparing a mode field adapter improved according to an embodiment of the present application. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0030] See also Figure 1, in an embodiment of the present application, a mode field adapter includes a first optical fiber 100 and a second optical fiber 200.

[0031] In this embodiment, refer to Figure 1 , the first optical fiber 100 includes a connected first optical fiber body 110 and a first connection section 120, and the first connection section 120 is located at one end of the first optical fiber body 110. The first optical fiber 100 is an integral structure of the first optical fiber body 110 and the first connection section 120. The first optical fiber 100 includes a core and a cladding, and the cladding wraps the core. Among them, the cladding can be provided with one layer or multiple layers, such as two layers of cladding. In addition, the first optical fiber body 110 further includes a coating layer, and the coating layer includes the cladding setting.

[0032] In this embodiment, refer to Figure 1 , the second optical fiber 200 includes a connected second optical fiber body 210 and a second connection section 220, and the second connection section 220 is located at one end of the second optical fiber body 210. The second optical fiber body 210 and the second connection section 220 of the second optical fiber 200 are an integral structure. The first optical fiber 100 is fusion spliced with the second optical fiber 200. Among them, the first connection section 120 and the second connection section 220 are located between the first optical fiber body 110 and the second optical fiber body 210, and one end of the first connection section 120 departing from the first optical fiber body 110 is fusion spliced with one end of the second connection section 220 departing from the second optical fiber body 210. The second optical fiber 200 includes a core and a cladding, and the cladding wraps the core. The cladding can be provided with one layer or multiple layers, such as two layers of cladding. In addition, the first optical fiber body 110 further includes a coating layer, and the coating layer includes the cladding setting.

[0033] Refer to Figure 1 , the core diameter of the first optical fiber body 110 is D1, the cladding diameter of the first optical fiber body 110 is S1, the core diameter of one end of the first connection section 120 departing from the first optical fiber body 110 is D2, and the cladding diameter is S2, the core diameter of the second optical fiber body 210 is D4 and the cladding diameter is S4, the core diameter of one end of the second connection section 220 departing from the second optical fiber body 210 is D3 and the cladding diameter is S3. Among them, S1 < S2 = S3 < S4, and D1 = D2 = D3 < D4.

[0034] In the embodiments of the present application, one end of the first optical fiber 100 is core-expanded to increase the core diameter of the end of the first optical fiber 100, and one end of the second optical fiber 200 is tapered to reduce the core diameter and the cladding diameter of the end of the second optical fiber 200, so as to realize the fusion splicing of the first optical fiber 100 and the second optical fiber 200. This is beneficial to the fusion splicing of the first connection section 120 and the second connection section 220. The difference in the core diameter between the first connection section 120 and the core of the first optical fiber body 110 is small, and the difference in the core diameter between the second connection section 220 and the core of the second optical fiber body 210 is small, and the difference in the cladding diameter is small. It has the advantages of easy fusion splicing operation, small fusion splicing loss, and good optical signal transmission.

[0035] In some embodiments, referring to Figure 1 , S1 = 10μm, D1 = 125μm, S4 = 30μm, D4 = 250μm.

[0036] It can be understood that the specification of the first optical fiber body 110 is 10 / 125, and the specification of the second optical fiber body 210 is 30 / 250. In the related art, only the end of the second optical fiber body 210 is tapered, and a specification with a core diameter of 10μm and a cladding diameter of 125μm cannot be prepared. After the tapering operation, if the core diameter is 10μm, the corresponding cladding diameter is 80μm to 100μm. It is impossible to perform a fusion splicing operation with the first optical fiber body 110. In this embodiment, after the first connection section 120 is core-expanded and the second connection section 220 is tapered to reduce the core diameter and the cladding diameter and then fused, the first optical fiber 100 and the second optical fiber 200 have good adaptability and the fusion splicing operation is simple.

[0037] In some embodiments, referring to Figure 1 , S2 = S3 = 15μm.

[0038] In the embodiments of the present application, the core diameter of the core-expanded first connection section 120 changes from 10μm to 15μm, the core diameter of the tapered second connection section 220 changes from 30μm to 15μm, the cladding diameter of the end of the tapered second connection section 220 is 125μm, and the processing operations of the first connection section 120 and the second connection section 220 are simple.

[0039] In some embodiments, referring to Figure 1, the core of the first connection segment 120 includes a first core segment 121 and a second core segment 122. The first core segment 121 is located between the first optical fiber body 110 and the second core segment 122, and the first core segment 121 connects the core of the first optical fiber body 110 and the second core segment 122. Among them, the core diameter of the second core segment 122 is S2, and along the direction from the first connection segment 120 to the second core segment 122, the diameter of the first core segment 121 gradually increases. Exemplarily, the diameter of the first core segment 121 gradually expands from 10 μm to 15 μm. The diameter of the second core segment 122 is 15 μm uniformly.

[0040] In the embodiments of the present application, referring to Figure 1 , the core of the first connection segment 120 includes a first core segment 121 and a second core segment 122. The core diameter of the first core segment 121 gradually expands, and the core diameters of the second core segment 122 are the same. The first connection segment 120 is prepared by core expansion, so that the highly doped particles in the core region diffuse into the cladding, increasing the effective core diameter of the optical fiber, thereby achieving the purpose of increasing the optical fiber mode field of the first optical fiber 100.

[0041] In some embodiments, along the length direction of the first optical fiber 100, the length of the first connection segment 120 is L1, and 3 mm ≤ L1 ≤ 3.5 mm. For example, the value of L1 is 3 mm, 3.1 mm, 3.2 mm, 3.3 mm, 3.4 mm, 3.5 mm or other unlisted values.

[0042] In the embodiments of the present application, the length of the first connection segment 120 is processed by the core expansion processing technology. The length of the first connection segment 120 is reasonably designed to ensure that the core expansion processing operation can be performed while avoiding material waste caused by the first connection segment 120 being too long, which is beneficial to the miniaturization of the device.

[0043] In some embodiments, referring to Figure 1 , the second connection segment 220 includes a first optical fiber segment 221 and a second optical fiber segment 222. The first optical fiber segment 221 is located between the second optical fiber body 210 and the second optical fiber segment 222, and the first optical fiber segment 221 connects the second optical fiber body 210 and the second optical fiber segment 222. Among them, the core diameter and the cladding diameter of the second optical fiber segment 222 are D3 and S3 respectively. Along the direction from the second optical fiber body 210 to the second optical fiber segment 222, both the cladding diameter and the core diameter of the first optical fiber segment 221 gradually decrease. Exemplarily, after the tapering operation, the cladding diameter of the first optical fiber segment 221 gradually shrinks from 250 μm to 125 μm, and the core diameter of the first optical fiber segment 221 gradually shrinks from 30 μm to 15 μm. The cladding diameter of the second optical fiber segment 222 is 125 μm uniformly, and the core diameter of the second optical fiber segment 222 is 15 μm uniformly.

[0044] In the embodiments of the present application, the core and the cladding of the first optical fiber section 221 adopt a gradually shrinking structure, and the first optical fiber section 221 is equivalent to the transition region between the second optical fiber body 210 and the second optical fiber section 222. The optical fiber section in the transition region adopts a gradient structure, and the mode field diameter of the second optical fiber 200 will gradually decrease from large to small. The probability of the situation that the mode in the core is converted into the cladding mode due to the change of the mode field not keeping up with the change of the optical fiber waveguide shape is reduced, thereby realizing low loss.

[0045] In some embodiments, referring to Figure 1 , the length of the second connection section 220 is L2, and 12.5 mm ≤ L2 ≤ 16.5 mm. Among them, the value of L2 is 12.5 mm, 13 mm, 14 mm, 15 mm, 16 mm, 16.5 mm or other unlisted values.

[0046] In the embodiments of the present application, the second connection section 220 is processed by a forward tapering operation. The length of the second connection section 220 is reasonably designed, which is convenient for the second connection section 220 to be processed and formed, and avoids the situation that the second connection section 220 is too long, wasting materials, increasing costs and device size.

[0047] In some embodiments, referring to Figure 1 , the length of the first optical fiber section 221 is l1, and 2.5 mm ≤ l1 ≤ 3.5 mm. Among them, the value of l2 is 2.5 mm, 2.6 mm, 2.8 mm, 3.0 mm, 3.2 mm, 3.5 mm or other unlisted values.

[0048] In the embodiments of the present application, the core diameter of the first optical fiber section 221 adopts a gradient structure, and the length of the first optical fiber section 221 is appropriate, avoiding the situation that the core diameter of the first optical fiber section 221 changes greatly due to the too short length of the first optical fiber section 221, resulting in the mode field change not keeping up with the optical fiber waveguide change and generating large losses. Nor will it be disadvantageous to the packaging, miniaturization and stability of the device due to the too long length of the first optical fiber section 221. The length of the first optical fiber section 221 in this embodiment reduces the material cost while meeting low loss, which is beneficial to device packaging and miniaturization.

[0049] In some embodiments, referring to Figure 1 , the length of the second optical fiber section 222 is l2, and 10 mm ≤ l2 ≤ 13 mm. The value of l2 is 10 mm, 11.6 mm, 11.8 mm, 12.0 mm, 12.5 mm, 13 mm or other unlisted values.

[0050] In some embodiments, referring to Figure 1 and Figure 2, the mode field adapter further includes a glass sleeve 300 sleeved on the connection of the first optical fiber 100 and the second optical fiber 200, covering at least the first connection section 120 and the second connection section 220.

[0051] Exemplarily, the coating layer of a part of the first connection section 120 on the first optical fiber 100 is stripped, and a stripping opening is formed at the connection of the first optical fiber body 110 and the second connection section 220. The coating layer of a part of the second connection section 220 on the second optical fiber 200 is stripped, and a stripping opening is formed at the connection of the second optical fiber body 210 and the second connection section 220. The glass sleeve 300 is sleeved on the first optical fiber 100 and the second optical fiber 200, covering at least the two stripping openings and the connection of the first connection section 120 and the second connection section 220.

[0052] In the embodiment of the present application, the stripping openings and the connection are protected by the glass sleeve 300, improving the reliability of the mode field adapter.

[0053] In some embodiments, referring to Figure 2 , the glass sleeve 300 is fixedly adhered to the first optical fiber 100 and the second optical fiber 200.

[0054] Exemplarily, a high-refractive-index glue is filled in the area between the stripping opening of the glass sleeve 300 and the first optical fiber 100 and the stripping opening of the second optical fiber 200, and the bare fiber and the stripping opening are glued and cured to protect the fusion point and strip the redundant cladding light. The glue does not fall off and the optical fiber does not break. The mode field adapter has been put into use in a pulsed laser, and no adverse phenomena such as high temperature and bright stripping opening are found in the test.

[0055] Referring to Figure 1 and Figure 3 , the embodiment of the present application also provides a preparation method of a mode field adapter for preparing the mode field adapter of any one of the above, including the following steps:

[0056] S1, providing a single-mode optical fiber and a large-mode field optical fiber;

[0057] Exemplarily, the specification of the single-mode optical fiber is that the core diameter is 10 μm and the cladding diameter is 125 μm, and the specification of the large-mode field optical fiber is that the core diameter is 30 μm and the cladding diameter is 250 μm.

[0058] S2, performing a core expansion process on the single-mode optical fiber to prepare the first optical fiber 100, where the first optical fiber 100 includes a connected first optical fiber body 110 and a first connection section 120, and the first connection section 120 is located at one end of the first optical fiber body 110;

[0059] Exemplarily, the core diameter of the first optical fiber body 110 of the first optical fiber 100 is 10 μm, and the cladding diameter is 125 μm. The core diameter of one end of the first connection section 120 departing from the first optical fiber body 110 is 15 μm, and the cladding diameter is 125 μm.

[0060] S3. Perform forward tapering on the large mode field optical fiber to prepare a second optical fiber 200. The second optical fiber 200 includes a connected second optical fiber body 210 and a second connection section 220. The second connection section 220 is located at one end of the second optical fiber body 210. The cladding diameter of one end of the second connection section 220 departing from the second optical fiber body 210 is the same as the cladding diameter of one end of the first connection section 120 departing from the first optical fiber body 110, and the core diameter of one end of the second connection section 220 departing from the second optical fiber body 210 is the same as the core diameter of one end of the first connection section 120 departing from the first optical fiber body 110.

[0061] Exemplarily, the core diameter of the second optical fiber body 210 of the second optical fiber 200 is 30 μm, and the cladding diameter is 250 μm. The core diameter of one end of the second connection section 220 departing from the second optical fiber body 210 is 15 μm, and the cladding diameter is 125 μm.

[0062] S4. Fuse the first optical fiber 100 and the second optical fiber 200.

[0063] Specifically, one end of the first connection section 120 departing from the first optical fiber body 110 is fused with one end of the second connection section 220 departing from the second optical fiber body 210.

[0064] In the embodiment of the present application, the core of the single-mode optical fiber is expanded to increase the core diameter at the end of the first optical fiber 100, and the large mode field optical fiber is tapered to reduce the core diameter and cladding diameter at the end of the second optical fiber 200, so as to realize the fusion of the first optical fiber 100 and the second optical fiber 200. It is beneficial to the fusion of the first connection section 120 and the second connection section 220. The difference in core diameter between the first connection section 120 and the first optical fiber body 110 is small, and the difference in core diameter and cladding diameter between the second connection section 220 and the second optical fiber body 210 is small, having the advantages of easy fusion operation, small fusion loss, and good optical signal transmission.

[0065] Exemplarily, taking the mode field adapter prepared by fusing an optical fiber with a specification of 10 / 125 and an optical fiber with a specification of 30 / 250 as an example, in Comparative Example 1, the 10 / 125 optical fiber and the 30 / 250 optical fiber are directly fused. In Comparative Example 2, after tapering the 30 / 250 optical fiber, it is fused with the 10 / 125 optical fiber. The cladding light and insertion loss are shown in the following table:

[0066]

[0067]

[0068] Compared with Comparative Example 1 and Comparative Example 2, the cladding light of the mode field adapter in the embodiment of the present application is less, and the insertion loss is lower.

[0069] In some embodiments, after the single-mode fiber is expanded by a fiber taper machine, the single-mode fiber is cut to prepare the first optical fiber 100. Among them, the parameters of the fiber taper machine are: the diameter of the flame head is 3 mm, the hydrogen flow rate is 130 sccm, the oxygen flow rate is 20 sccm, the moving length of the flame head is 3 mm, and the heating duration is 360 s.

[0070] Specifically, the single-mode fiber is fixed by a fixture, and the flame head of the fiber taper machine reciprocates along the middle of the single-mode fiber. The flame head of the fiber taper machine moves 3 mm left and right along the midpoint position to avoid making the fiber brittle due to heating at one point. After processing, the flame head is removed. After cooling, it is cut along the midpoint position to prepare the first optical fiber 100. The temperature is high and the temperature change is small at the center of the flame head of the flame. When heating the optical fiber, the structure of the second core segment 122 in the first connection segment 120 is formed, and the structure of the first core segment 121 is formed at the position far from the flame head where the temperature drops.

[0071] In some embodiments, after the large mode field fiber is positively tapered by a fiber taper machine, the large mode field fiber is cut to prepare the second optical fiber 200; among them, the parameters of the fiber taper machine are: the diameter of the flame head is 3 mm, the hydrogen flow rate is 116 sccm, the oxygen flow rate is 20 sccm, the moving length of the flame head is 12.5 mm, and the tapering length of the large mode field fiber is 15 mm.

[0072] Specifically, the large mode field fiber is clamped and fixed by a fixture, and the large mode field fiber is heated by the flame of the fiber taper machine. During the heating process, the fixture moves to apply a tensile force to the large mode field fiber to stretch and thin the fiber. When the length of the large mode field fiber increases by 15 mm, the heating and the movement of the fixture are stopped. After the large mode field fiber cools down, it is cut at a position 22.5 mm away from the stripping port of the large mode field fiber to prepare the second optical fiber 200.

[0073] In some embodiments, before the single-mode fiber is expanded, a section of the coating layer on the single-mode fiber is stripped. The removal length of the coating layer is 3 cm.

[0074] In some embodiments, before the large mode field fiber is reduced in core, a section of the coating layer on the large mode field fiber is stripped. The removal length of the coating layer is 3 cm.

[0075] In the above embodiments, the descriptions of each embodiment have their own focuses. For the parts not detailed in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0076] In the description of the present application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more features.

[0077] The above has introduced in detail the mode field adapter provided by the embodiments of the present application. Specific examples are used herein to elaborate on the principle and implementation manner of the present application. The description of the above embodiments is only used to help understand the method and its core idea of the present application; at the same time, for those skilled in the art, according to the idea of the present application, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present application.

Claims

1. A mode field adapter, characterized in that: include: A first optical fiber (100) comprises a first optical fiber body (110) and a first connecting section (120) which are connected, wherein the first connecting section (120) is located at one end of the first optical fiber body (110); A second optical fiber (200), comprising a second optical fiber body (210) and a second connecting section (220) connected to each other, wherein the second connecting section (220) is located at one end of the second optical fiber body (210), and an end of the first connecting section (120) facing away from the first optical fiber body (110) is fused with an end of the second connecting section (220) facing away from the second optical fiber body (210); A glass sleeve (300), wherein the glass sleeve (300) is sleeved at the connection between the first optical fiber (100) and the second optical fiber (200), and covers at least the first connecting section (120) and the second connecting section (220); The core diameter and cladding diameter of the first optical fiber body (110) are D1 and S1 respectively, the core diameter and cladding diameter of the end of the first connecting section (120) away from the first optical fiber body (110) are D2 and S2 respectively, the core diameter and cladding diameter of the second optical fiber body (210) are D4 and S4 respectively, and the core diameter and cladding diameter of the end of the second connecting section (220) away from the second optical fiber body (210) are D3 and S3 respectively, wherein: S1<S2=S3<S4, and D1=D2=D3<D4.

2. The mode field adapter according to claim 1, characterized in that: S1=10μm, D1=125μm, S4=30μm, D4=250μm.

3. The mode field adapter according to claim 2, characterized in that: S2=S3=15μm.

4. The mode field adapter according to claim 1, characterized in that: The fiber core of the first connecting section (120) comprises a first fiber core section (121) and a second fiber core section (122), the first fiber core section (121) is located between the first optical fiber body (110) and the second fiber core section (122), the first fiber core section (121) connects the fiber core of the first optical fiber body (110) and the second fiber core section (122), wherein: The core diameter of the second core segment (122) is S2, and along the direction from the first connecting segment (120) to the second core segment (122), the diameter of the first core segment (121) gradually increases.

5. The mode field adapter according to claim 1, characterized in that: Along the length direction of the first optical fiber (100), the length of the first connecting section is L1, 3mm≤L1≤3.5mm.

6. The mode field adapter according to claim 1, characterized in that: The second connecting segment (220) comprises a first optical fiber segment (221) and a second optical fiber segment (222); the first optical fiber segment (221) is located between the second optical fiber body (210) and the second optical fiber segment (222); the first optical fiber segment (221) connects the second optical fiber body (210) and the second optical fiber segment (222); the core diameter and cladding diameter of the second optical fiber segment (222) are D3 and S3 respectively; and along the direction from the second optical fiber body (210) to the second optical fiber segment (222), the cladding diameter and the core diameter of the first optical fiber segment (221) both gradually decrease.

7. The mode field adapter according to claim 6, characterized in that: The length of the first optical fiber segment (221) is l1, 2.5 mm ≤ l1 ≤ 3.5 mm; And / or, the length of the second optical fiber segment (222) is l2, 10mm≤l2≤13mm.

8. The mode field adapter according to claim 1, characterized in that: The length of the second connecting section (220) is L2, 12.5 mm ≤ L2 ≤ 16.5 mm.

9. The mode field adapter according to claim 1, characterized in that: The glass sleeve (300) is fixed to the first optical fiber (100) and the second optical fiber (200) by gluing.

10. The mode field adapter according to claim 1, characterized in that: The second optical fiber (200) is manufactured by using a forward taper process.

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