Active homogenizing optical fiber

Abstract

The invention provides an active homogenized optical fiber which comprises a fiber core layer and a cladding arranged around the fiber core layer, the refractive index of the fiber core layer is larger than that of the cladding, the fiber core layer comprises silicate materials doped with rare earth elements, and the fiber core layer is provided with a fiber core disturbance shape and / or a fiber core disturbance structure. And the fiber core disturbance shape or the fiber core disturbance structure is configured to be used for improving the homogenization effect of the light beam in the fiber core layer. Compared with a passive homogenized optical fiber, the active homogenized optical fiber has the advantages that light spot homogenization can be realized under the condition of the same length, the length requirement of the passive homogenized optical fiber is avoided, and the system design is simplified; meanwhile, homogenization is directly achieved in the active optical fiber, passive optical fiber parts needing to be welded and processed are reduced, the requirement for the melting point of the optical fiber can be lowered, and the overall length of the optical fiber is reduced; in addition, the gain characteristic of the active homogenized optical fiber not only provides an amplification effect, but also can effectively improve the nonlinear threshold of the active homogenized optical fiber.

Description

Technical Field

[0001] The present invention relates to the field of gain fibers, and in particular to an active homogenizing fiber. Background Art

[0002] The beam intensity of the laser output by a fiber laser is usually Gaussian-like distributed in space, that is, the central intensity is the highest, and the intensity around gradually decreases according to the Gaussian distribution. In practical applications, when the Gaussian-like beam acts on the processing surface, the energy density at the center of the light spot is much greater than that at the edge of the light spot, thus affecting the consistency of the processing effect at different positions along the diameter of the light spot within the light spot. Especially when femtosecond lasers with Gaussian-like energy distribution are used for metal material processing, the low energy density at the edge of the light spot will cause a relatively serious thermal burning effect on the surface of the metal material, which may lead to defects such as cracks and sputtering. During laser coating and laser cleaning processes, a uniform beam can ensure the uniformity and cleanliness of the processing surface, improve efficiency and reduce unnecessary material loss. In laser illumination systems and medical laser treatments, a uniform beam distribution can improve the uniformity of irradiation, reduce thermal damage to the target area, and enhance the overall effect. Therefore, changing the energy distribution of the laser beam, especially converting the Gaussian-like beam into a uniform beam, has important practical significance in many applications and can effectively improve the processing accuracy and quality.

[0003] At the present stage, the homogenization effect of the beam is usually achieved by introducing a section of passive homogenizing fiber. In order to obtain sufficient homogenization effect, a relatively long passive fiber is often required, which not only increases the volume and complexity of the system, but also leads to more insertion losses. Especially in high-power laser applications, an overly long passive fiber may cause higher energy losses. The fiber will bear a certain thermal load during operation. Since the energy of high-power laser is transmitted through the fiber, heat will be generated. If the melting point of the fiber is too low, or the fiber material does not have sufficient heat dissipation capacity, it may lead to a decline in the performance of the fiber, or even melting or burning. Due to the manufacturing and structural differences of the fiber, the passive fiber may introduce mode distortion, resulting in an irregular distribution of the output beam, thus affecting the final homogenization effect. In addition, factors such as the attenuation and insertion loss of the passive fiber will also introduce certain uncertainties. As the length of the passive fiber increases, the distribution of the laser power density in the fiber may cause thermal accumulation in some areas, affecting the stability and quality of the output beam.

[0004] Therefore, there is an urgent need for an active homogenizing fiber to solve the above technical problems. Summary of the Invention

[0005] The purpose of the present invention is to provide an active homogenizing fiber, which is used to solve the technical problem that a relatively high fiber length is required for the passive fiber in the prior art to achieve the homogenization of the light spot.

[0006] The present application provides an active homogenizing optical fiber, which includes a core layer and a cladding disposed around the core layer. The refractive index of the core layer is greater than that of the cladding. The core layer includes a silicate material doped with rare earth elements. Wherein, the core layer has a core perturbation shape and / or a core perturbation structure, and the core perturbation shape or the core perturbation structure is configured to improve the homogenization effect of the light beam in the core layer.

[0007] Preferably, when the core layer has a core perturbation shape, the cross-section of the core layer along the vertical radial direction is a polygon.

[0008] Preferably, when the core layer has a core perturbation structure, the cross-section of the core layer along the vertical radial direction is any one of a polygon, a circle, and a semi-annular shape.

[0009] Preferably, the core perturbation structure is embedded in the core layer, and the core perturbation structure sequentially includes a first perturbation layer and a second perturbation layer from the inside to the outside along the vertical radial direction. Wherein, the refractive index of the second perturbation layer is less than that of the first perturbation layer.

[0010] Preferably, the absolute value of the difference between the refractive index of the first perturbation layer and the refractive index of the core layer is less than or equal to 0.01, and the refractive index of the first perturbation layer is greater than that of the cladding.

[0011] Preferably, the active homogenizing optical fiber further includes a low refractive index structure disposed between the core layer and the cladding. The low refractive index structure surrounds the core layer and adheres to the outer surface of the core layer. Wherein, the absolute value of the difference between the refractive index of the low refractive index structure and the refractive index of the second perturbation layer is less than or equal to 0.01, and the refractive index of the low refractive index structure is less than that of the first perturbation layer.

[0012] Preferably, the absolute value of the difference between the refractive index of the cladding and the refractive index of the core layer is less than or equal to 0.01, and the absolute value of the difference between the refractive index of the first perturbation layer and the refractive index of the cladding is less than or equal to 0.01.

[0013] Preferably, the first perturbation layer includes a silicate material doped with rare earth elements, and the second perturbation layer and the low refractive index structure are both any one of a fluorine-doped silicate material and an air hole layer.

[0014] Preferably, the core perturbation structure is embedded in the core layer, the cross-section of the core perturbation structure along the vertical radial direction is a semi-annular shape, and the material of the core perturbation structure is Si.

[0015] Preferably, the core perturbation structure is concentrically arranged with the core layer.

[0016] The beneficial effects of the present invention are as follows: Different from the prior art, the present invention provides an active homogenizing optical fiber, which includes a core layer and a cladding disposed around the core layer. The refractive index of the core layer is greater than that of the cladding. The core layer includes a silicate material doped with rare earth elements. Among them, the core layer has a core perturbation shape and / or a core perturbation structure, and the core perturbation shape or the core perturbation structure is configured to improve the homogenization effect of the light beam in the core layer. The above-mentioned active homogenizing optical fiber has the following advantages compared with the passive homogenizing optical fiber: Firstly, the active homogenizing optical fiber can achieve spot homogenization under the same length, avoiding the length requirement of the passive homogenizing optical fiber and simplifying the system design; Secondly, by directly realizing homogenization in the active optical fiber, the part of the passive optical fiber that needs to be fused and processed is reduced, which helps to reduce the melting point requirement of the optical fiber and reduce the overall length of the optical fiber; Thirdly, the gain characteristic of the active homogenizing optical fiber not only provides an amplification effect, but also may effectively increase its nonlinear threshold; Compared with traditional optical fibers, under higher power conditions, the presence of the gain medium can suppress the undesired nonlinear effects, thereby improving the stability and performance of the system; Fourthly, through the design of the optical fiber and the optimization of the gain medium, the light beam can be more evenly distributed in the core, which helps to improve the quality and stability of the output light beam, especially in high-power laser transmission, avoiding the influence of spot fluctuations on the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 FIG. is a schematic cross-sectional structure diagram of the active homogenizing optical fiber provided in Embodiment 1 of the present invention; Figure 2 FIG. is a schematic cross-sectional structure diagram of the active homogenizing optical fiber provided in Embodiment 2 of the present invention; Figure 3 FIG. is a schematic cross-sectional structure diagram of the active homogenizing optical fiber provided in Embodiment 3 of the present invention; In the drawings: 100 - active homogenizing optical fiber; 10 - core layer; 20 - cladding; 30 - core perturbation structure; 31 - first perturbation layer; 32 - second perturbation layer; 40 - low refractive index structure. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] Next, the technical solutions in this embodiment will be clearly and completely described in conjunction with this embodiment. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0019] Aiming at the technical problem that the passive optical fiber in the prior art requires a relatively high optical fiber length to achieve spot homogenization, the present invention provides an active homogenizing optical fiber to solve the above technical problem.

[0020] The present invention proposes the concept of an active homogenizing optical fiber, which integrates active gain and homogenization to achieve a uniform distribution of light beams. The combination of gain and beam homogenization enables the gain medium in the optical fiber to provide active gain, effectively amplifying the signal light during propagation. The design of the optical fiber ensures that the light beam can be evenly distributed throughout the core, avoiding the Gaussian-like distribution in traditional active optical fibers. Due to the uniform distribution of the light beam throughout the core, the signal light can be extracted more efficiently, avoiding signal loss caused by uneven mode distribution in traditional active optical fibers.

[0021] Please refer to Figures 1 to 3 , this application provides an active homogenizing optical fiber 100, including a core layer 10 and a cladding 20 disposed around the core layer 10. The refractive index of the core layer 10 is greater than that of the cladding 20. The core layer 10 includes a silicate material doped with rare earth elements (such as Yb and other rare earth elements). Among them, the core layer 10 has a core perturbation shape and / or a core perturbation structure 30, and the core perturbation shape or the core perturbation structure 30 is configured to enhance the homogenization effect of the light beam within the core layer 10.

[0022] In the first embodiment, when the core layer 10 has a core perturbation shape, the cross-section of the core layer 10 along the vertical radial direction is a polygon. The core perturbation shape is not limited to a square and also includes various other shapes such as a rectangle, a hexagon, an octagon, and a star shape, etc.

[0023] Specifically, the cross-section of the core layer 10 along the vertical radial direction being a polygon can promote beam homogenization, mainly for the following reasons: Destroying the circular symmetry structure: The polygon cross-section destroys the circular symmetry structure of the core cross-section, making the light rays in the core in a chaotic state. This chaotic state will excite more high-order modes. Compared with a circular core, a polygon core can allow light to experience more different paths and modes during transmission, and the mode coupling between high-order modes is stronger. As a result, the energy at the core center can be dispersed to the periphery, achieving spot homogenization.

[0024] Increasing reflection and refraction: The multiple sides of the polygon will cause the light rays to undergo more reflections and refractions within the core. When the light rays are reflected and refracted between different sides, their propagation directions and intensity distributions will change continuously. The cumulative effect of multiple reflections and refractions enables the energy of the light beam to be more evenly distributed across the entire core cross-section, reducing the situation where energy is concentrated at the center or certain specific regions, thereby promoting beam homogenization.

[0025] In the second embodiment, when the core layer 10 has the core perturbation structure 30, the cross-section of the core layer 10 along the vertical radial direction is any one of a polygon, a circle, and a semi-annular shape. At this time, the core perturbation structure 30 is configured as a core perturbation rod for actively homogenizing the optical fiber 100, and the core perturbation rod can promote beam homogenization. The main reasons are as follows: When the light beam is transmitted in the core layer 10, due to the core perturbation rod, the refractive index of the core layer 10 changes, the Gaussian energy distribution is destroyed, and higher-order modes are excited. Mode coupling occurs between these higher-order modes and the fundamental mode, so that the energy can be evenly dispersed from the original concentrated Gaussian distribution to the periphery, realizing beam homogenization.

[0026] Specifically, the core perturbation structure 30 is embedded in the core layer 10. The core perturbation structure 30 sequentially includes a first perturbation layer 31 and a second perturbation layer 32 from the inside to the outside along the vertical radial direction. The refractive index of the second perturbation layer 32 is less than that of the first perturbation layer 31; the absolute value of the difference between the refractive index of the first perturbation layer 31 and the refractive index of the core layer 10 is less than or equal to 0.01 (the refractive index of the first perturbation layer 31 is approximately equal to the refractive index of the core layer 10), and the refractive index of the first perturbation layer 31 is greater than the refractive index of the cladding 20.

[0027] Furthermore, the refractive index of the first perturbation layer 31 is close to that of the core layer 10, which means that when the light beam enters the first perturbation layer 31 from the core layer 10, due to the small change in refractive index, the light beam will not undergo obvious refraction or scattering, so that it can maintain good transmission characteristics, reduce the interference with the transmission direction and energy distribution of the light beam, and ensure the efficient transmission of the light beam in the core. The refractive index of the first perturbation layer 31 is greater than the refractive index of the cladding 20, so that a structure similar to the core-cladding 20 is formed between the first perturbation layer 31 and the cladding 20. According to the principle of fiber optics, when light propagates in a high-refractive-index medium, it will be constrained by the low-refractive-index cladding 20 and restricted within the core region. Therefore, the first perturbation layer 31 can play a certain role in constraining the light beam, preventing the light beam from leaking into the cladding 20 prematurely, and improving the transmission efficiency and stability of the light beam in the core.

[0028] Furthermore, the refractive index of the second perturbation layer 32 is less than that of the first perturbation layer 31. This refractive index difference will perturb the light beam, changing the propagation direction and energy distribution of the light beam. Since the second perturbation layer 32 is embedded in the core layer 10, this perturbation occurs inside the core, which can effectively break the original distribution of the light beam in the core, promote the redistribution of the energy of the light beam in the core, and thus achieve the effect of beam homogenization. At the same time, the combined structure of the first perturbation layer 31 and the second perturbation layer 32 can make the perturbation effect more controllable and stable. By adjusting parameters such as the refractive index difference and the respective thicknesses of the two layers, the effect of beam homogenization can be optimized.

[0029] Specifically, the active homogenizing optical fiber 100 further includes a low refractive index structure 40 disposed between the core layer 10 and the cladding layer 20. The low refractive index structure 40 surrounds the core layer 10 and adheres to the outer surface of the core layer 10. Wherein, the absolute value of the difference between the refractive index of the low refractive index structure 40 and the refractive index of the second perturbation layer 32 is less than or equal to 0.01, and the refractive index of the low refractive index structure 40 is less than the refractive index of the first perturbation layer 31.

[0030] Furthermore, the low refractive index structure 40 is located between the core layer 10 and the cladding layer 20, and its refractive index is less than that of the first perturbation layer 31, which helps to further confine the light beam within the regions of the core layer 10 and the first perturbation layer 31. Since light reflects when it encounters an interface with a lower refractive index during propagation in a medium with a higher refractive index, this structure can reduce the possibility of the light beam leaking into the cladding layer 20, improving the transmission efficiency and stability of the light beam within the core. At the same time, the refractive index of the low refractive index structure 40 is close to that of the second perturbation layer 32, meaning that they have a certain synergy in the action on the light beam. When the light beam propagates from the core layer 10 to the second perturbation layer 32 and then to the low refractive index structure 40, due to the continuous change in refractive index, the light beam will be continuously perturbed, thereby more effectively breaking the original energy distribution of the light beam and promoting the more uniform distribution of the light beam energy within the region composed of the core layer 10, the first perturbation layer 31, the second perturbation layer 32, and the low refractive index structure 40, achieving a better light beam homogenization effect.

[0031] Specifically, the absolute value of the difference between the refractive index of the cladding layer 20 and the refractive index of the core layer 10 is less than or equal to 0.01, and the absolute value of the difference between the refractive index of the first perturbation layer 31 and the refractive index of the cladding layer 20 is less than or equal to 0.01. Among them, the refractive index differences between the first perturbation layer 31 and the cladding layer 20, and the core layer 10 are very small. When the light beam travels from the core layer 10 into the first perturbation layer 31 and then to the cladding layer 20, it will experience multiple slight refractive index changes. Each refractive index change will cause a slight change in the propagation direction and intensity distribution of the light beam, and the cumulative effect of these slight changes will gradually disperse the energy of the light beam into a larger area, thereby achieving light beam homogenization. At the same time, this refractive index distribution makes it easier for mode coupling to occur between different modes in the optical fiber. Moreover, due to the relatively small refractive index change, the mode coupling process is relatively stable and will not cause unstable phenomena such as mode competition, which is beneficial to achieving stable light beam homogenization.

[0032] Specifically, the first perturbation layer 31 includes a silicate material doped with rare earth elements (such as Yb or other rare earth elements), and both the second perturbation layer 32 and the low refractive index structure 40 are any one of fluorine-doped silicate materials and air hole layers.

[0033] Furthermore, the refractive index of fluorine-doped silicate materials is low, and the refractive index of the material can be reduced by doping fluorine into the silicate material. As another optional material, the air hole layer has a refractive index close to 1, which is much lower than that of the silicate material. The introduction of an air hole layer in the optical fiber can form a strong refractive index contrast, which has a strong scattering and disturbing effect on the light beam. The size, shape and distribution of the air holes can be precisely designed to achieve fine control of the light beam homogenization effect. For example, by changing the spacing and diameter of the air holes, the scattering angle and intensity of the light beam in the air hole layer can be adjusted, so that the light beam energy is more evenly distributed on the cross section of the optical fiber. In addition, the air hole layer can also reduce the weight of the optical fiber, improve the flexibility of the optical fiber, and facilitate the laying and application of the optical fiber.

[0034] In another embodiment of the present invention, the core disturbance structure 30 is embedded in the core layer 10, the cross section of the core disturbance structure 30 along the vertical radial direction is semi-annular, and the material of the core disturbance structure 30 is Si.

[0035] Specifically, the semi-annular Si core perturbation structure 30 will destroy the symmetry of light propagation in the optical fiber, resulting in enhanced coupling between different modes. During the transmission process, the light will undergo mode conversion under the action of the semi-annular structure, and the energy originally concentrated in certain specific modes will be dispersed into other modes. For example, the energy of some high-order modes may be transferred to low-order modes, or vice versa, making the energy distribution of the light beam between different modes more uniform, thereby achieving homogenization of the light beam in the cross section.

[0036] Specifically, the core perturbation structure 30 is concentrically arranged with the core layer 10; the concentric arrangement makes the effect of the core perturbation structure 30 on the light beam symmetrical. No matter from which direction the light beam enters the core, the perturbation effect is uniform in all directions. This avoids the situation where the light beam is excessively perturbed in some directions and insufficiently perturbed in other directions due to the eccentricity of the perturbation structure, thereby ensuring the stability and consistency of the light beam homogenization effect.

[0037] The technical solution of the present application is now described in conjunction with specific embodiments.

[0038] Embodiment 1: See also Figure 1 This embodiment 1 provides an active homogenized optical fiber 100 with a square core and other core shapes, and the cross section of the optical fiber is as follows: Figure 1 As shown, it includes a core layer 10 and a cladding layer 20 arranged around the core layer 10, the refractive index n1 of the core layer 10 is greater than the refractive index n2 of the cladding layer 20, the core layer 10 includes a silicate material doped with rare earth elements (doped with Yb and other rare earth elements), the cladding layer 20 is a quartz material, and the light beam is uniformly distributed in the core layer 10 of the shape of a square core doped with rare earth elements; Among them, the core layer 10 has a core perturbation shape. The cross-section of the core layer 10 along the vertical radial direction is a polygon. The core perturbation shape is not limited to a square, but also includes various other shapes such as a rectangle, a hexagon, an octagon, and a star, etc.

[0039] Specifically, Embodiment 1 provides specific preparation steps for an active homogenized optical fiber 100 structure with a square core and other shaped cores (such as hexagon, star, etc.) prepared by the MCVD (Modified Chemical Vapor Deposition) process as follows: (1) Use a 25*3*900 high-purity quartz tube as the reaction tube, introduce 60 sccm SF6 to corrode the inner wall and remove the inner wall impurities. Then introduce 200 sccm SiO2 gas into the reaction tube, and deposit a barrier layer on the inner wall and polish it under the action of a hydrogen-oxygen flame at 2100 °C.

[0040] (2) Introduce 250 sccm SiO2 gas and 10 sccm SF6 gas into the reaction tube, and deposit a loose quartz layer under the action of a hydrogen-oxygen flame at 1600 °C respectively.

[0041] (3) Remove the reaction tube after depositing the loose layer, and introduce a doped ion solution. Soak for 30 - 60 min, and the rotation speed of the quartz tube is 65 r / min. The porous structure inside the quartz tube will adsorb the ions in the solution, and rotation will promote the absorption of ions by the porous structure.

[0042] (4) Drain the solution from the quartz tube and dry it with nitrogen to obtain a doped quartz tube containing elements such as Yb.

[0043] (5) Pass 180 sccm Cl2 through the loose layer after solution doping to dry and remove the moisture and hydroxyl groups in the tube, pass 1100 sccm high-purity oxygen to oxidize to obtain Yb oxide, and vitrify and sinter it under the action of a hydrogen-oxygen flame at 2200 °C.

[0044] (6) Repeat steps (2), (3), (4), and (5) several times; subject the reaction tube after depositing the core layer 10 to melt shrinkage under the action of a hydrogen-oxygen flame at 2400 °C to form a solid optical fiber preform.

[0045] (7) Grind the optical fiber preform to obtain a square core or other shaped cores.

[0046] (8) Polish the ground optical fiber preform once under a hydrogen-oxygen flame at 1850 °C.

[0047] (9) Assemble the optical fiber preform with a quartz sleeve, and draw a square-core homogenized active optical fiber with a certain outer diameter through a drawing tower.

[0048] Embodiment 2: Embodiment 2 provides a core-embedded homogenized active optical fiber, the structure of which is as Figure 2 shown. The above-mentioned core-embedded homogenized active optical fiber includes a core layer 10 and a cladding layer 20 arranged around the core layer 10. The refractive index of the core layer 10 is greater than that of the cladding layer 20. The core layer 10 includes a silicate material doped with rare earth elements (such as other rare earth elements like Yb), and the cladding layer 20 is a quartz material; Among them, the core layer 10 has a core perturbation structure 30. The core perturbation structure 30 includes a first perturbation layer 31 and a second perturbation layer 32 in sequence from the inside to the outside along the vertical radial direction; the active homogenized optical fiber 100 further includes a low refractive index structure 40 arranged between the core layer 10 and the cladding layer 20. The low refractive index structure 40 surrounds the core layer 10 and adheres to the outer surface of the core layer 10.

[0049] Further, the first perturbation layer 31 includes a silicate material doped with rare earth elements, and the second perturbation layer 32 and the low refractive index structure 40 are both any one of fluorine-doped silicate materials and air hole layers.

[0050] Further, the refractive index n5 of the second perturbation layer 32 is less than the refractive index n7 of the first perturbation layer 31. The absolute value of the difference between the refractive index n7 of the first perturbation layer 31 and the refractive index n4 of the core layer 10 is less than or equal to 0.01. The absolute value of the difference between the refractive index n6 of the cladding layer 20 and the refractive index n4 of the core layer 10 is less than or equal to 0.01. The absolute value of the difference between the refractive index n5 of the first perturbation layer 31 and the refractive index n8 of the cladding layer 20 is less than or equal to 0.01 (the refractive indices basically satisfy n4≈n6≈n7>n5≈n8).

[0051] Specifically, Embodiment 2 provides the following specific preparation steps for preparing a core-embedded homogenized active optical fiber by the MCVD process: (1) Use a 25*3*900 high-purity quartz tube as the reaction tube, introduce 60 sccm SF6 to corrode the inner wall and remove the inner wall impurities. Then introduce 200 sccm SiO2 gas into the reaction tube, and deposit a barrier layer on the inner wall under the action of a 2100℃ oxyhydrogen flame and polish it.

[0052] (2) Introduce 250 sccm SiO2 gas and 20 sccm SF6 gas into the reaction tube, deposit a porous quartz layer under the action of a 1600℃ oxyhydrogen flame respectively and polish and sinter it, and repeat the deposition of the fluorine-doped passive layer several times.

[0053] (3) Introduce 250 sccm SiO2 gas and 10 sccm SF6 gas into the reaction tube, and deposit a porous quartz layer under the action of a 1600℃ oxyhydrogen flame respectively.

[0054] (4) Remove the reaction tube with the loose layer deposited, and introduce the doped ion solution. Soak for 30 - 60 min, and the rotation speed of the quartz tube is 65 r / min. The porous structure inside the quartz tube will adsorb the ions in the solution, and rotation will promote the absorption of ions by the porous structure.

[0055] (5) Drain the solution from the quartz tube and dry it with nitrogen to obtain a doped quartz tube containing elements such as Yb.

[0056] (6) Pass 180 sccm of Cl₂ into the loose layer after solution doping to dry and remove the moisture and hydroxyl groups inside the tube, then pass 1100 sccm of high-purity oxygen for oxidation to obtain Yb oxide and vitrification sintering under the action of a 2200 °C hydrogen-oxygen flame.

[0057] (7) Repeat steps (3), (4), (5), and (6) several times; subject the reaction tube with the core layer 10 deposited to melt contraction under the action of a 2400 °C hydrogen-oxygen flame to form a solid fiber preform.

[0058] (8) Sleeve and reduce the fiber preform prepared by MCVD and the quartz sleeve in proportion to form a large core rod.

[0059] (9) Drill a 4-mm pore in the core part of the large core rod obtained in step (8), and the pore deviates from the core for standby.

[0060] (10) Take another core rod prepared by MCVD, grind off the outer pure quartz layer with a grinder, and then draw the core rod to a diameter of 3 mm.

[0061] (11) Assemble the core perturbation rod prepared in step (10) and the preform prepared in step (9) for wire drawing to obtain a core-embedded homogenized active fiber.

[0062] Example 3: This Example 3 provides a core-embedded homogenized active fiber, and its structure is as Figure 3 shown. The above-mentioned core-embedded homogenized active fiber includes a core layer 10 and a cladding 20 arranged around the core layer 10. The refractive index of the core layer 10 is greater than that of the cladding 20. The core layer 10 includes a silicate material doped with rare earth elements (such as Yb and other rare earth elements), and the cladding 20 is made of quartz material; Among them, the core layer 10 has a core perturbation structure 30. The cross-section of the core perturbation structure 30 along the vertical radial direction is semi-circular. The material of the core perturbation structure 30 is Si, and the core perturbation structure 30 is concentrically arranged with the core layer 10.

[0063] Specifically, this Example 3 provides the following specific preparation steps for preparing a core-embedded homogenized active fiber by the MCVD process: (1) Use a 25*3*900 high-purity quartz tube as the reaction tube, introduce 60 sccm of SF6 to corrode the inner wall and remove impurities on the inner wall. Then introduce 200 sccm of SiO2 gas into the reaction tube, and deposit a barrier layer on the inner wall under the action of a hydrogen-oxygen flame at 2100 °C and polish it.

[0064] (2) Introduce 250 sccm of SiO2 gas and 10 sccm of SF6 gas into the reaction tube, and deposit a porous quartz layer under the action of a hydrogen-oxygen flame at 1600 °C respectively.

[0065] (3) Remove the reaction tube with the deposited porous layer, and introduce a doped ion solution. Immerse for 30 - 60 min, and the rotation speed of the quartz tube is 65 r / min. The porous structure inside the quartz tube will adsorb the ions in the solution, and rotation will promote the absorption of ions by the porous structure.

[0066] (4) Drain the solution from the quartz tube and dry it with nitrogen to obtain a doped quartz tube containing elements such as Yb.

[0067] (5) Pass 180 sccm of Cl2 through the porous layer after solution doping to dry and remove moisture and hydroxyl groups in the tube, then pass 1100 sccm of high-purity oxygen to oxidize to obtain Yb oxide and vitrify and sinter under the action of a hydrogen-oxygen flame at 2200 °C.

[0068] (6) Repeat steps (2), (3), (4), and (5) several times; subject the reaction tube with the deposited core layer 10 to fusion shrinkage under the action of a hydrogen-oxygen flame at 2400 °C to form a solid first optical fiber preform.

[0069] (7) Use a 25*3*900 high-purity quartz tube as the reaction tube, introduce 60 sccm of SF6 to corrode the inner wall and remove impurities on the inner wall. Then introduce 200 sccm of SiO2 gas into the reaction tube, and deposit a barrier layer on the inner wall under the action of a hydrogen-oxygen flame at 2100 °C and polish it.

[0070] (8) Introduce 250 sccm of SiO2 gas and 10 sccm of SF6 gas into the reaction tube, and deposit a porous quartz layer under the action of a hydrogen-oxygen flame at 1600 °C respectively.

[0071] (9) Remove the reaction tube with the deposited porous layer, and introduce a doped ion solution. Immerse for 30 - 60 min, and the rotation speed of the quartz tube is 65 r / min. The porous structure inside the quartz tube will adsorb the ions in the solution, and rotation will promote the absorption of ions by the porous structure.

[0072] (10) Drain the solution from the quartz tube and dry it with nitrogen to obtain a doped quartz tube containing elements such as Yb.

[0073] (11) After doping the solution into the loose layer, successively introduce 180 sccm of Cl2 to dry and remove the moisture and hydroxyl groups in the tube, introduce 1100 sccm of high-purity oxygen for oxidation to obtain Yb oxide, and vitrify and sinter it under the action of a hydrogen-oxygen flame at 2200 °C.

[0074] (12) Repeat steps (8), (9), (10), and (11) four times.

[0075] (13) Introduce 250 sccm of SiO2 gas into the reaction tube, deposit a loose quartz layer under the action of a hydrogen-oxygen flame at 1600 °C respectively, and then immediately vitrify and sinter it under the action of a hydrogen-oxygen flame at 2200 °C.

[0076] (14) Repeat steps (8), (9), (10), and (11) two times.

[0077] (15) Subject the reaction tube deposited with the core layer 10 to melt shrinkage under the action of a hydrogen-oxygen flame at 2400 °C to form a solid second optical fiber preform.

[0078] (16) Divide the first optical fiber preform and the second optical fiber preform into two along the core layer 10 respectively.

[0079] (17) Combine and fix half of the first optical fiber preform and half of the second optical fiber preform.

[0080] (18) Draw the active homogenized optical fiber 100 through a fiber drawing tower.

[0081] Currently, the calculation formula for the optical fiber uniformity is I min / I max × 100% (I min is the minimum light intensity value in the measurement area, and I max is the maximum light intensity value in the measurement area). The core energy of the traditional active optical fiber shows a Gaussian distribution, and its uniformity is about 60%. The uniformity of the active homogenized optical fiber 100 with a square core and other shaped cores provided in this Embodiment 1 is about 85%, and the uniformity of the core-embedded homogenized active optical fiber provided in this Embodiment 2 or this Embodiment 3 is about 92%.

[0082] Different from the prior art, the present invention proposes an active homogenized optical fiber 100, which combines gain and beam homogenization. The gain medium in the optical fiber provides active gain, enabling the signal light to be effectively amplified during propagation, and the design of the optical fiber ensures that the beam can be evenly distributed throughout the core, avoiding the Gaussian distribution in the traditional active optical fiber.

[0083] Specifically, the specific advantages of the active homogenized optical fiber 100 provided by the present invention are as follows: 1. Traditional passive optical fibers require a long fiber length to achieve spot homogenization, while the active homogenizing optical fiber 100 can achieve spot homogenization under the same length, avoiding the length requirement of passive homogenizing optical fibers and simplifying the system design.

[0084] 2. By directly implementing homogenization in the active optical fiber, the part of the passive optical fiber that needs to be fused and processed is reduced, which helps to lower the melting point requirement of the optical fiber and reduce the overall length of the optical fiber. This is particularly important for high-power laser applications because long optical fibers are prone to additional losses and heat accumulation.

[0085] 3. The gain characteristics of the active homogenizing optical fiber 100 not only provide an amplification effect but also may effectively increase its nonlinear threshold. Compared with traditional optical fibers, in the case of higher power, the presence of the gain medium can suppress unwanted nonlinear effects, thereby improving the stability and performance of the system.

[0086] 4. Through the design of the optical fiber and the optimization of the gain medium, the light beam can be more evenly distributed within the core, which helps to improve the quality and stability of the output light beam, especially in high-power laser transmission, avoiding the influence of spot fluctuations on the system.

[0087] It should be noted that the above embodiments all belong to the same inventive concept. The descriptions of the embodiments have their own emphases. For the parts not described in detail in individual embodiments, reference can be made to the descriptions in other embodiments.

[0088] The above embodiments only represent the implementation manners of the present invention. Their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those of ordinary skill in the art, without departing from the inventive concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent should be subject to the appended claims.

Claims

1. An active homogenizing optical fiber, characterized in that, It includes a core layer and a cladding layer disposed around the core layer. The refractive index of the core layer is greater than that of the cladding layer. The core layer includes a rare-earth element-doped silicate material; Wherein, the core layer has a core perturbation shape and / or a core perturbation structure, and the core perturbation shape or the core perturbation structure is configured to enhance the homogenization effect of the light beam within the core layer.

2. The active homogenizing optical fiber according to claim 1, wherein When the core layer has the core perturbation shape, the cross-section of the core layer along the vertical radial direction is a polygon.

3. The active homogenizing optical fiber according to claim 1, wherein, When the core layer has the core perturbation structure, the cross-section of the core layer along the vertical radial direction is any one of a polygon, a circle, and a semi-annular shape.

4. The active homogenizing optical fiber according to claim 3, wherein The core perturbation structure is embedded in the core layer, and the core perturbation structure sequentially includes a first perturbation layer and a second perturbation layer from the inside to the outside along the vertical radial direction; Wherein, the refractive index of the second perturbation layer is less than that of the first perturbation layer.

5. The active homogenizing optical fiber according to claim 4, wherein The absolute value of the difference between the refractive index of the first perturbation layer and the refractive index of the core layer is less than or equal to 0.01, and the refractive index of the first perturbation layer is greater than that of the cladding layer.

6. The active homogenizing optical fiber according to claim 4, wherein The active homogenization optical fiber further includes a low refractive index structure disposed between the core layer and the cladding layer. The low refractive index structure surrounds the core layer and adheres to the outer surface of the core layer; Wherein, the absolute value of the difference between the refractive index of the low refractive index structure and the refractive index of the second perturbation layer is less than or equal to 0.01, and the refractive index of the low refractive index structure is less than that of the first perturbation layer.

7. The active homogenizing optical fiber according to claim 6, wherein, The absolute value of the difference between the refractive index of the cladding layer and the refractive index of the core layer is less than or equal to 0.01, and the absolute value of the difference between the refractive index of the first perturbation layer and the refractive index of the cladding layer is less than or equal to 0.

01.

8. The active homogenizing optical fiber according to claim 6, characterized in that The first perturbation layer includes a rare-earth element-doped silicate material, and the second perturbation layer and the low refractive index structure are both any one of a fluorine-doped silicate material and an air hole layer.

9. The active homogenizing optical fiber according to claim 3, wherein The core perturbation structure is embedded in the core layer, the cross-section of the core perturbation structure along the vertical radial direction is semi-annular, and the material of the core perturbation structure is Si.

10. The active homogenizing optical fiber according to claim 9, wherein, The core perturbation structure is concentrically arranged with the core layer.

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