Homogenized optical fiber and optical fiber laser

Abstract

Disclosed in the embodiments of the present application are a homogenized optical fiber and an optical fiber laser. The homogenized optical fiber comprises an optical fiber core and an optical fiber cladding that are sequentially arranged from the inside to the outside, wherein the refractive index of the optical fiber core is higher than the refractive index of the optical fiber cladding, the optical fiber core is sequentially provided with an optical fiber inner core, a doped layer and an optical fiber outer core from the inside to the outside, and the refractive index of the doped layer is lower than the refractive indexes of the optical fiber inner core and the optical fiber outer core. By embedding a doped layer within an optical fiber core instead of filling the entire central region of the optical fiber core, the homogenization effect of an optical fiber can be effectively improved on the basis of ensuring that the structure of an optical fiber body is simple.

Description

A homogenized optical fiber and a fiber laser

[0001] This application claims priority to the Chinese patent application No. 202410707231.X filed on June 03, 2024 with the Chinese Patent Office, the whole content of the above application is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of fiber lasers, in particular to a homogenized optical fiber and a fiber laser. BACKGROUND

[0003] Since entering the 21st century, lasers have been widely used in various industries, and various types of lasers have emerged in an endless stream. Among them, fiber lasers stand out due to their excellent beam quality, high stability, and flexible output, and have replaced traditional gas and solid-state lasers in many fields in just a few decades. As a type of fiber laser, high-power continuous fiber lasers have been particularly prominent in the field of industrial processing in recent years, replacing traditional flame and plasma processing equipment, and gradually replacing carbon dioxide lasers. With the development of technology and the emergence of new demands, fiber lasers in the field of industrial processing are not limited to sheet metal processing, but also extend to composite welding, additive manufacturing, material modification, and other new high-end fields. The requirements for lasers in these emerging fields are gradually increasing, especially in terms of output beam form, leading to the development of a series of beam shaping solutions to meet different application needs.

[0004] For standard continuous fiber lasers, the form is generally divided into single-module lasers and multi-module lasers composed of multiple single-module lasers. Single-module lasers have high beam quality and Gaussian or quasi-Gaussian beam output, while multi-module lasers generally have high power and poor beam quality, with output beams tending to be flat-top beams. Gaussian beams are not as effective as flat-top beams in some processing fields, especially in additive manufacturing, so multi-module lasers are often used in additive manufacturing. However, multi-module lasers are not suitable for some applications due to their poor beam quality. In order to obtain flat-top beams with high beam quality, many solutions have been proposed by researchers and engineers in recent years, including two main directions: the first is to optimize the internal optical path of the fiber laser, which has the advantages of simple structure, easy production, and low cost, but the disadvantages are weak homogenization ability, high beam quality degradation, and poor consistency of batch products. The other is to adjust the external optical path, which has high consistency, controllable beam quality change, and good homogenization effect, but the disadvantages are high cost and complex structure. SUMMARY

[0005] At present, a new homogenization optical fiber is urgently needed to optimize the optical path inside the optical fiber, ensure that the main structure of the optical fiber changes little, realize the homogenization function, and ensure the output of high beam quality flat top (or homogenization) beam.

[0006] The embodiment of the present application provides a homogenization optical fiber to solve the technical problem that the optical fiber in the prior art cannot simultaneously ensure that the main structure of the optical fiber is simple and the homogenization effect is good.

[0007] In a first aspect, to solve the above technical problem, the embodiment of the present application provides a homogenization optical fiber, which comprises an optical fiber core and an optical fiber cladding arranged in sequence from inside to outside, and the refractive index of the optical fiber core is higher than the refractive index of the optical fiber cladding.

[0008] The optical fiber core is sequentially provided with an optical fiber inner core, a doped layer and an optical fiber outer core from inside to outside, and the refractive index of the doped layer is lower than the refractive index of the optical fiber inner core and the optical fiber outer core.

[0009] In the embodiment of the present application, the doped layer is a continuous annular region.

[0010] In the embodiment of the present application, the shape of the annular region is a regular polygon.

[0011] In the embodiment of the present application, the shape of the annular region is a square, a regular pentagon or a regular hexagon.

[0012] In the embodiment of the present application, the annular region is a fluorine-doped region.

[0013] In the embodiment of the present application, the annular wall thickness of the annular region is not greater than 20 microns.

[0014] In the embodiment of the present application, the annular wall thickness of the annular region is 5-10 microns.

[0015] In the embodiment of the present application, the light collecting capacity of the annular region is 0.01-0.22.

[0016] In the embodiment of the present application, the materials of the optical fiber inner core and the optical fiber outer core are pure quartz.

[0017] In the embodiment of the present application, the optical fiber cladding comprises a first cladding and a second cladding.

[0018] The first cladding is a fluorine layer, and the second cladding is a pure silica layer.

[0019] In the embodiment of the present application, the homogenization optical fiber further comprises an optical fiber coating layer, and the optical fiber coating layer is arranged outside the optical fiber cladding.

[0020] In the embodiment of the present application, the material of the optical fiber coating layer is any one of an acrylic resin layer, a polyimide layer and a silicone rubber layer.

[0021] In a second aspect, the embodiments of the present application further provide a fiber laser, comprising a homogenization fiber, the homogenization fiber comprising a fiber core and a fiber cladding arranged in sequence from inside to outside, the refractive index of the fiber core being higher than the refractive index of the fiber cladding.

[0022] The fiber core is arranged in sequence from inside to outside with a fiber inner core, a doped layer, and a fiber outer core, the refractive index of the doped layer being lower than the refractive index of the fiber inner core and the fiber outer core.

[0023] In the embodiments of the present application, the doped layer is a continuous annular region.

[0024] In the embodiments of the present application, the shape of the annular region is a regular polygon.

[0025] In the embodiments of the present application, the annular region is a fluorine-doped region.

[0026] In the embodiments of the present application, the annular region has a ring wall thickness of no more than 20 microns.

[0027] In the embodiments of the present application, the annular region has a ring wall thickness of 5-10 microns.

[0028] In the embodiments of the present application, the light collecting capability of the annular region is 0.01-0.22.

[0029] In the embodiments of the present application, the fiber cladding comprises a first cladding and a second cladding.

[0030] The first cladding is a fluorine layer, and the second cladding is a pure silica layer. Advantages

[0031] The embodiments of the present application provide a homogenization fiber and a fiber laser, the homogenization fiber comprising a fiber core and a fiber cladding arranged in sequence from inside to outside, the refractive index of the fiber core being higher than the refractive index of the fiber cladding, the fiber core being arranged in sequence from inside to outside with a fiber inner core, a doped layer, and a fiber outer core, the refractive index of the doped layer being lower than the refractive index of the fiber inner core and the fiber outer core. By embedding a doped layer in the fiber core instead of filling the entire central region of the fiber core, the homogenization effect of the fiber can be effectively improved on the basis of ensuring that the main structure of the fiber is simple. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative effort on the basis of these drawings.

[0033] Fig. 1 is a structure and refractive index profile of a germanium core energy delivery fiber in the related art;

[0034] Fig. 2a is a structure and refractive index profile of a pure silicon core energy delivery fiber in the related art;

[0035] Fig. 2b is another structure and refractive index profile of a pure silicon core energy delivery fiber in the related art;

[0036] Fig. 3 is a homogenization fiber structure and refractive index profile in the related art;

[0037] Fig. 4 is a structure of a homogenization fiber according to an embodiment of the present application;

[0038] Fig. 5 is a structure of a homogenization fiber according to an embodiment of the present application;

[0039] Fig. 6 is a light path of a homogenization fiber according to an embodiment of the present application in a 3000W fiber laser;

[0040] Fig. 7 is an original beam quality and focal spot energy distribution of a 3000W fiber laser (without homogenization fiber);

[0041] Fig. 8 is a beam quality and focal spot energy distribution of a homogenization fiber according to an embodiment of the present application in a 3000W fiber laser;

[0042] Fig. 9 is a beam quality and focal spot energy distribution of a homogenization fiber in the related art in a 3000W fiber laser. Embodiments of the present application

[0043] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0044] In the description of the present application, it needs to be understood that the orientation or positional relationship indicated by the terms "longitudinal", "transverse", "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal" and the like is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element indicated must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" are only for description purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise explicitly specified. In the present application, " / " represents the meaning of "or".

[0045] The present application can repeatedly refer to numbers and / or letters in different examples, and such repetition is for the purpose of simplification and clarity, and does not indicate the relationship between the various embodiments and / or arrangements discussed.

[0046] In the embodiments of the present application, lasers have been widely used in various industries, and various different types of lasers have emerged in an endless stream. Among the many lasers, fiber lasers stand out due to their excellent beam quality, high stability, and flexible output, and other outstanding advantages. From the invention of fiber lasers to the widespread replacement of traditional gas and solid lasers, it has only taken a few decades. High-power continuous fiber lasers, as one of the fiber lasers, have been particularly prominent in the industrial processing field in recent years, not only replacing traditional flame and plasma processing equipment, but also gradually replacing carbon dioxide lasers. With the development of technology and the emergence of new demands, fiber lasers in the industrial processing field are no longer limited to plate processing, but also extend to composite welding, additive manufacturing, material modification and other new high-end fields. In these emerging fields, the requirements for lasers are gradually increasing, especially in the form of output beams, thus developing a series of beam shaping schemes to meet different application needs.

[0047] In the related art, the energy transfer fiber in the high-power laser can be divided into two categories according to whether the core is doped:

[0048] The first type is to realize high refractive index of the fiber core by doping germanium in the fiber core, so as to limit the transmission of light in the fiber core, which is called a germanium core optical fiber, and is generally used for communication or low-power transmission. Due to the doping process and doping characteristics, the core of the optical fiber is relatively small, and the core size is generally several microns to tens of microns, and it is usually a single-mode or few-mode optical fiber. Specifically, as shown in FIG. 1, FIG. 1 is a structure and refractive index profile diagram of a germanium core energy transmission optical fiber in the related art, wherein the black area 101 is a germanium-doped area.

[0049] The second type is to realize a low refractive index region by doping fluorine on the periphery of a pure silicon core or fusing and shrinking a fluorine-doped quartz tube, so as to realize a relatively high refractive index of the fiber core, thereby limiting the transmission of light in the fiber core, which is called a pure silicon core energy transmission optical fiber. Because the fluorine-doped layer is thin and the core is pure silica, this kind of optical fiber can realize large core diameter transmission, and the core can be from tens of microns to thousands of microns. This type of optical fiber is generally used for high-power laser transmission. As shown in FIG. 2a, FIG. 2a is a structure and refractive index profile diagram of a pure silicon core energy transmission optical fiber in the related art, wherein the core 201 is a pure silicon core, and the black area 202 is a fluorine-doped area. In some cases, in order to increase the strength, part of the second type of optical fiber will increase a layer of silica as a cladding 203 outside the fluorine-doped area 202, as shown in FIG. 2b, which is another structure and refractive index profile diagram of a pure silicon core energy transmission optical fiber in the related art.

[0050] In order to realize flat-top beam output, the related art also provides a homogenization optical fiber that can realize flat-top beam output, please refer to FIG. 3, which is a homogenization optical fiber structure and refractive index profile diagram in the related art. The function of the homogenization optical fiber is to convert the originally transmitted Gaussian or Gaussian-like beam into a flat-top beam. Its general implementation is to introduce a low refractive index region 301 in the pure silicon core 302 on the basis of the pure silicon core energy transmission optical fiber, and the refractive index difference (or NA) between the region 301 and the core 302 is very low. By utilizing the tendency of light to transmit in a high refractive region in a waveguide, part of the central transmitted energy is transferred to the edge, that is, the central energy in the base film (LP01) and part of the circular symmetric mode (LP0n) is scattered, so as to realize the change of energy distribution. By using different homogenization optical fibers, flat-top beam output can be realized.

[0051] However, the central low refractive index region of this type of homogenization optical fiber is generally realized by fluorine doping process, and due to the influence of the process, it is difficult to make the region very large, which limits the adjustment of modes other than LP0n. On the other hand, it is also difficult to achieve perfect uniformity, which leads to insufficient homogenization degree of the output light spot or light spot deviation, and even deterioration of beam quality.

[0052] For the standard continuous fiber laser, its form is generally divided into single module laser and multiple module laser composed of multiple single module lasers. The single module laser has high beam quality, Gaussian or Gaussian-like beam output; the multiple module laser generally has higher power, and the output beam quality is larger, and the output beam tends to be a flat-top beam. The Gaussian beam is used in some processing fields, especially in additive manufacturing, and its effect is not as good as that of the flat-top beam, so additive manufacturing usually uses multiple module lasers, but the multiple module laser is not suitable for some applications due to poor beam quality. In order to obtain a flat-top beam with high beam quality, in recent years, many researchers and engineers have proposed many schemes, which include two large directions: the first is to optimize the internal optical path of the fiber laser, which has the advantages of simple structure, easy production, low cost, and the disadvantages of weak homogenization ability, high beam quality deterioration, and poor consistency of batch products; the other is to adjust the external optical path, which has the advantages of high consistency and controllable beam quality change, and the disadvantage of high cost and complex structure.

[0053] Therefore, there is an urgent need for a new homogenization fiber to optimize the internal optical path of the fiber laser, to ensure that the main structure of the current laser changes little, to realize the homogenization function, and to ensure the output of a high beam quality flat-top (or homogenization) beam.

[0054] In order to solve the above technical problems, the embodiments of the present application provide a homogenization fiber and a fiber laser. Specifically, please refer to FIG. 4, which is a structural schematic diagram of the homogenization fiber provided by the embodiments of the present application. FIG. 4 shows a cross-sectional structure of the homogenization fiber provided by the embodiments of the present application, and the refractive index change curve corresponding to each layer structure of the homogenization fiber (each layer structure is marked with a corresponding refractive index curve by a dashed line). As shown in FIG. 4, the homogenization fiber provided by the embodiments of the present application includes a fiber core (401, 402, 403) and a fiber cladding (404, 405) arranged in order from inside to outside. The refractive index of the fiber core is higher than that of the fiber cladding. The fiber core is sequentially provided with a fiber inner core 401, a doped layer 402, and a fiber outer core 403 from inside to outside. The refractive index of the doped layer 402 is lower than that of the fiber inner core 401 and the fiber outer core 403.

[0055] Since the fiber core of the present embodiment is sequentially provided with the fiber inner core 401, the doped layer 402, and the fiber outer core 403 from inside to outside, and the refractive index of the doped layer 402 is lower than that of the fiber inner core 401 and the fiber outer core 403, the embodiments of the present application can introduce structural and refractive index perturbations into the fiber core at the same time, use the low refractive index doped layer 402 to perturb the low order mode to excite high order modes, and convert part of the base film and low order mode energy into high order core modes, thereby shaping the Gaussian or Gaussian-like beam, and finally realizing the output of a homogenized spot.

[0056] In some embodiments, the doping layer 402 provided by the embodiments of the present application can be a continuous annular region. Specifically, the annular region is a regular polygon, please refer to FIG. 5, which is a plurality of structural schematic diagrams of the homogenization optical fiber provided by the embodiments of the present application. As shown in FIG. 5, the annular region provided by the embodiments of the present application can be a square 501, a regular pentagon 502, a regular hexagon 503, etc. The regular polygon can further ensure the output of the homogenization light spot.

[0057] In order to ensure that the refractive index of the doping layer 402 is lower than the refractive index of the inner core 401 and the outer core 403 of the optical fiber, in the embodiments of the present application, fluorine is doped in the annular region 402 to form a fluorine-doped region, and pure quartz is used as the inner core 401 and the outer core 403 of the optical fiber. In this way, the refractive index of the doping layer 402 can be lower than the refractive index of the inner core 401 and the outer core 403 of the optical fiber, so that the light tends to be transmitted in the high-refractive region in the waveguide, part of the central transmission energy is transferred to the edge, the energy distribution is changed, and finally the flat-top light beam output is realized.

[0058] Meanwhile, the introduction of any homogenization optical fiber will inevitably lead to the deterioration of the beam quality. However, the conventional homogenization optical fiber directly regulates the central energy, which will lead to the serious deterioration of the beam quality, because the main energy of the Gaussian or Gaussian-like light beam is distributed in the center. The homogenization optical fiber provided by the embodiments of the present application has the same pure quartz with uniform refractive index in the central region as the conventional energy transmission optical fiber, which can effectively avoid the main energy region of the Gaussian light beam and gently disturb the main energy region, so that the deterioration of the beam quality is small.

[0059] Optionally, in the optical fiber core of the homogenization optical fiber provided by the embodiments of the present application, the inner core 401 and the outer core 403 of the optical fiber can be pure quartz layers, and the doping layer 402 can be a fluorine layer, that is, the optical fiber core of the homogenization optical fiber provided by the embodiments of the present application can only contain pure quartz and fluorine, so the homogenization optical fiber provided by the embodiments of the present application can belong to a typical passive optical fiber.

[0060] In some embodiments, the thickness of the annular wall of the annular region 402 provided by the embodiments of the present application is not greater than 20 microns, and the NA (numerical aperture, used to describe the light transmission or light collection capability of the optical fiber) of the annular region is 0.01-0.22.

[0061] In the related art, the homogenization fiber is usually a low refractive index region in the center of the fiber core by doping process, the diameter of the low refractive index region is tens of microns, and the size of the region is very close to the limit of the doping ability. The NA is generally between 0.001 and 0.01, and the NA range is very small and needs to be accurately controlled. However, too small NA cannot achieve homogenization effect, and too large NA will cause the energy of the center of the light spot to be completely depressed, so that the final effect cannot meet the requirements.

[0062] The homogenization fiber provided in the embodiments of the present application is obtained by embedding a continuous annular region 402 in the fiber core, the diameter of the annular region is not more than 20 microns, and the typical value can be 5-10 microns, and the NA range is between 0.01 and 0.22. With the current doping process, it is easy to achieve, so as to effectively ensure that the main structure of the homogenization fiber is simple and easy to produce.

[0063] In the embodiments of the present application, in order to limit the transmission of the fiber core light in the fiber core, the fiber cladding provided in the embodiments can include a first cladding 404 and a second cladding 405, the first cladding 404 is a fluorine layer, and the second cladding 405 is a pure silica layer.

[0064] As an optional embodiment, the homogenization fiber further includes a fiber coating layer (not shown in the figure), which is arranged outside the fiber cladding, and the material of the fiber coating layer is any one of an acrylic resin layer, a polyimide layer, and a silicone rubber layer.

[0065] Therefore, compared with the homogenization fiber in the related art, the homogenization fiber provided in the embodiments of the present application not only can reduce the difficulty of the doping process in the fiber to make the fiber easy to produce, but also can ensure that the beam quality degradation is small. Moreover, by using the double modulation of the structure and the refractive index, compared with the simple refractive index modulation of the homogenization fiber in the related art, the homogenization fiber provided in the embodiments of the present application is easier to achieve better homogenization effect.

[0066] In other embodiments, in order to better illustrate the homogenization fiber provided in the embodiments of the present application, which has better effect than the homogenization fiber in the related art, please also refer to FIG. 2b, FIG. 3, FIG. 4, FIG. 6, FIG. 7, FIG. 8 and FIG. 9. FIG. 6 is a kind of optical path schematic diagram of homogenization fiber provided in the embodiments of the present application in 3000W fiber laser, FIG. 7 is the original beam quality and focal spot energy distribution schematic diagram of 3000W fiber laser (without homogenization fiber), FIG. 8 is the beam quality and focal spot energy distribution schematic diagram of homogenization fiber provided in the embodiments of the present application in 3000W fiber laser, and FIG. 9 is the beam quality and focal spot energy distribution schematic diagram of homogenization fiber provided in the related art in 3000W laser.

[0067] Specifically, please refer to FIG. 2b and FIG. 6, the standard energy transmission fiber 602 with a fluorine layer in FIG. 6 is a pure silicon core energy transmission fiber provided in the related art, the model of the standard energy transmission fiber 602 is 50 / 70 / 360, and the cross section 603 of the standard energy transmission fiber 602 is shown in FIG. 2b. The diameter of the core 201 of the standard energy transmission fiber 602 is 50 microns; the first cladding layer 202 of the standard energy transmission fiber 602 is a fluorine layer, the thickness of the fluorine layer is 10 microns, the outer diameter of the fluorine layer is 70 microns, and the NA is 0.22; and the second cladding layer 203 of the standard energy transmission fiber 602 is pure silicon dioxide, and the outer diameter of the second cladding layer 203 is 360 microns.

[0068] Please refer to FIG. 3 and FIG. 6, the homogenized fiber 607 with a core containing a low refractive index region in FIG. 6 is a homogenized fiber provided in the related art, that is, the homogenized fiber shown in FIG. 3, wherein the fluorine core 301 is a low-fluorine-doped layer, the outer core 302 is pure silicon dioxide, the homogenization region 301 and the outer core 302 together form a core, the diameter of the core is 50 microns, the first cladding layer 303 is a fluorine-doped layer, the NA is 0.22, the outer diameter of the first cladding layer 303 is 70 microns, the second cladding layer 304 is pure silicon dioxide, and the outer diameter of the second cladding layer 304 is 360 microns.

[0069] Please refer to FIG. 4 and FIG. 6, the homogenized fiber 606 in FIG. 6 is a homogenized fiber provided in the embodiments of the present application, that is, the homogenized fiber shown in FIG. 4, wherein the inner core 401 of the fiber is pure silicon dioxide, the square fluorine layer 402 is a fluorine-doped layer, the NA is 0.12, the inner side length of the square fluorine layer 402 is 25 microns, the thickness of the fluorine layer is 5 microns, and the outer side length of the square fluorine layer 402 is 35 microns; the outer core 403 of the fiber is pure silicon dioxide, and the diameter of the outer core 403 is 50 microns; the inner core 401 of the fiber, the square fluorine layer 402, and the outer core 403 of the fiber together form a core of the homogenized fiber, and the total diameter of the core is 50 microns; the first cladding layer 404 is a fluorine layer ring for limiting the transmission of the core light in the core, and the thickness of the fluorine layer is 10 microns, that is, the outer diameter of the first cladding layer 404 is 70 microns; the second cladding layer 405 is pure silicon dioxide, and the outer diameter of the second cladding layer 405 is 360 microns.

[0070] As shown in FIG. 6, the 3000W laser 601 outputs a standard energy transmission fiber 602 (a pure silicon core energy transmission fiber 603), that is, a 50-micron core output, and a traditional laser directly outputs through a transmission cable 608, and the output is a Gaussian-like light spot as shown in 604, and the original beam quality (M2) of the laser is 3.37. Specifically, the beam quality report and the focal point energy distribution result of the traditional laser directly output through the transmission cable 608 are shown in FIG. 7.

[0071] If the 3000W laser 601 needs to be homogenized, the standard energy transmission fiber 602 is disconnected, and a homogenized fiber is inserted at the homogenized fiber insertion point 605.

[0072] In one embodiment, the homogenizing optical fiber 606 provided by the embodiment of the present application can be inserted at the homogenizing optical fiber insertion point 605, and a flat-top homogenized light spot energy distribution as shown in 609 can be obtained. Specifically, the beam quality (M2) of the laser obtained by using the homogenizing optical fiber 606 provided by the embodiment of the present application is 4.69, and the detailed beam quality report and the energy distribution at the focal point are shown in FIG. 8.

[0073] In another embodiment, the conventional energy transmission optical fiber 607 can also be inserted at the homogenizing optical fiber insertion point 605, and a semi-homogenized light spot energy distribution as shown in 610 can be obtained. Specifically, the beam quality (M2) of the laser obtained by using the homogenizing optical fiber provided in the related art is 5.48, and the detailed beam quality report and the energy distribution at the focal point are shown in FIG. 9.

[0074] From the homogenization effect, the focal point light spot output by the homogenizing optical fiber provided by the embodiment of the present application tends to be a flat-top light spot, while the focal point light spot output by the homogenizing optical fiber provided in the related art is still close to a Gaussian light beam, and the homogenization effect is limited. Therefore, the homogenization effect of the homogenizing optical fiber provided by the embodiment of the present application is better than that of the homogenizing optical fiber provided in the related art. From the output beam quality, after using the homogenizing optical fiber provided by the embodiment of the present application, the beam quality deteriorates from 3.37 to 4.69, and the deterioration rate is 1.39 times. After using the homogenizing optical fiber provided in the related art, the beam quality deteriorates from 3.37 to 5.48, and the deterioration rate is 1.62 times. Therefore, the deterioration rate of the beam quality of the laser by the homogenizing optical fiber provided by the embodiment of the present application is also better than that of the homogenizing optical fiber provided in the related art.

[0075] In summary, the embodiment of the present application provides a homogenizing optical fiber, which comprises a fiber core and a fiber cladding arranged in sequence from inside to outside, the refractive index of the fiber core is higher than that of the fiber cladding, the fiber core is sequentially provided with a fiber inner core, a doped layer and a fiber outer core from inside to outside, and the refractive index of the doped layer is lower than that of the fiber inner core and the fiber outer core.

[0076] Compared with the homogenizing optical fiber provided in the related art, the homogenizing optical fiber provided by the embodiment of the present application has the following advantages:

[0077] 1. The process difficulty is greatly reduced: the homogenization optical fiber provided in the related art is often introduced by a doping process in the center of the fiber core to introduce a low refractive index region, and the region diameter is in tens of microns. The size of the region is very close to the limit of the doping capacity. The NA is generally between 0.001 and 0.01, and the NA range is very small and needs to be accurately controlled. Too small cannot achieve homogenization effect, and too large will cause the central energy of the light spot to be completely recessed, so that the final effect cannot meet the requirements. The homogenization optical fiber provided in the embodiments of the present application is introduced by introducing a thin wall layer in the fiber core. The thin wall layer has a diameter of not more than 20 microns, and a typical value of 5-10 microns, and an NA range of 0.01-0.22. With the current doping process, it is easy to achieve;

[0078] 2. The light beam quality deterioration is controllable: the introduction of any homogenization optical fiber inevitably leads to deterioration of the light beam quality. However, the conventional homogenization optical fiber is disturbed to the central energy of the transmission light beam, and for a Gaussian or Gaussian-like light beam, the main energy is distributed in the center. Direct regulation of the central energy will cause serious deterioration of the light beam quality. The homogenization optical fiber provided in the embodiments of the present application has the same central region as the transmission energy optical fiber provided in the related art, which is a pure quartz with uniform refractive index, and can avoid the main energy region of the Gaussian light beam, so that the main energy region is disturbed gently, and the light beam quality deterioration is small.

[0079] 3. The homogenization effect is good: the embodiments of the present application adopt double modulation of structure and refractive index, which is easier to achieve better homogenization effect than the ordinary homogenization optical fiber with single refractive index modulation.

[0080] Some embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other.

[0081] The above is only a specific embodiment of the present application, which enables those skilled in the art to understand or implement the present application. Various modifications of 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 these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features applied herein.

Claims

1. A homogenizing optical fiber, wherein, The fiber core is provided with a fiber inner core, a doping layer and a fiber outer core from inside to outside, and the refractive index of the doping layer is lower than that of the fiber inner core and the fiber outer core. The doping layer is a continuous annular region.

2. The homogenizing optical fiber of claim 1, wherein, The annular region is a regular polygon.

3. The homogenizing optical fiber of claim 2, wherein, The annular region is a fluorine-doped region.

4. The homogenizing optical fiber of claim 2, wherein, The annular region has a ring wall thickness of no more than 20 microns.

5. The homogenizing optical fiber of claim 2, wherein, The annular region has a ring wall thickness of 5-10 microns.

6. The homogenizing optical fiber of claim 2, wherein, The annular region has a light collection capacity of 0.01-0.

22.

7. The homogenizing optical fiber of claim 6, wherein, The fiber inner core and the fiber outer core are made of pure quartz.

8. The homogenizing optical fiber of claim 2, wherein, The fiber cladding includes a first cladding and a second cladding.

9. The homogenizing optical fiber of claim 1, wherein, The first cladding is a fluorine layer, and the second cladding is a pure silica layer.

10. The homogenizing optical fiber of claim 1, wherein, The homogenized fiber further includes a fiber coating layer provided outside the fiber cladding. The fiber coating layer is made of any one of an acrylic resin layer, a polyimide layer and a silicone rubber layer.

11. The homogenizing optical fiber of claim 1, wherein, The fiber core is provided with a fiber inner core, a doping layer and a fiber outer core from inside to outside, and the refractive index of the doping layer is lower than that of the fiber inner core and the fiber outer core.

12. The homogenizing optical fiber of claim 11, wherein, The doping layer is a continuous annular region.

13. A fiber laser, wherein, The annular region is a regular polygon. The annular region is a fluorine-doped region.

14. The fiber laser of claim 13, wherein, The annular region has a ring wall thickness of no more than 20 microns.

15. The fiber laser of claim 14, wherein, The annular region has a ring wall thickness of 5-10 microns.

16. The fiber laser of claim 14, wherein, The annular region has a light collection capacity of 0.01-0.

22.

17. The fiber laser of claim 14, wherein, The fiber cladding includes a first cladding and a second cladding.

18. The fiber laser of claim 17, wherein, The first cladding is a fluorine layer, and the second cladding is a pure silica layer.

19. The fiber laser of claim 14, wherein, ​ 20. The fiber laser of claim 13, wherein, ​ ​

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