Gain fiber with low numerical aperture and stable absorptivity, fiber laser and laser processing equipment

Abstract

The invention relates to the field of laser processing, and discloses a gain optical fiber with low numerical aperture and stable absorptivity, an optical fiber laser and laser processing equipment, the gain optical fiber comprises a gain fiber core, a step layer and a cladding, the refractive index of the gain fiber core, the refractive index of the step layer and the refractive index of the cladding are sequentially reduced, the gain optical fiber has stable pump light absorptivity at the wave band of 900-1000 nm, and the step layer and the gain fiber core form a low numerical aperture structure. The gain optical fiber with low numerical aperture and stable absorptivity has high absorptivity for pump light in a wide wavelength range, the influence of the fluctuation of the central wavelength of the pump light on the light output power of the gain optical fiber is reduced, and the stability of the power output by the gain optical fiber is improved; the step layer is arranged between the cladding and the gain fiber core, so that the numerical aperture of the gain fiber core is reduced, the laser output with high beam quality is maintained, the unstable power threshold of a transverse mode is increased, and the optical coupling efficiency and the stability of the transverse mode output by the gain fiber are improved.

Description

Technical Field

[0001] The present application relates to the field of laser processing, and in particular to a gain optical fiber with low numerical aperture and stable absorption rate, an optical fiber laser and laser processing equipment. Background Art

[0002] In the field of laser processing, 915nm and 976nm semiconductor lasers are often used as pump sources for fiber lasers to pump gain fibers. However, the absorption rate of gain fibers to pump light with central wavelengths of 915nm and 976nm is unstable. In particular, the absorption rate of gain fibers decreases in the 930nm to 960nm band. When the central wavelength of the pump source fluctuates, the absorption rate changes, and the pump light cannot be completely absorbed, affecting the stability of the power output by the gain fiber. At the same time, the pump light that cannot be completely absorbed becomes heat energy in the subsequent optical path, wasting light energy and forming a heat source in the optical path where the gain fiber is located.

[0003] There are gain fibers doped with phosphorus on the market, which have a relatively stable absorption rate for pump light in the wavelength band of 915nm-970nm. However, phosphorus doping increases the numerical aperture of the fiber core. The higher numerical aperture reduces the transverse mode instability threshold of the gain fiber, affecting the stability of the transverse mode output by the gain fiber.

[0004] Therefore, it is necessary to propose a gain fiber, a fiber laser, and a laser processing device with a low numerical aperture and a stable absorption rate to maintain the output power and the stability of the transverse mode of the fiber laser. Summary of the invention

[0005] The present application proposes a gain fiber, fiber laser, and laser processing equipment with low numerical aperture and stable absorption rate. While solving the problems of narrow absorption spectrum of light in the 915nm and 976nm bands and unstable absorption of gain fiber in the prior art used in the field of laser processing, the gain fiber maintains a low numerical aperture, maintains laser output with high beam quality, and improves light coupling efficiency. The gain fiber proposed in the present application is applied in a fiber laser, and has low requirements on the wavelength stability of the pump source, and a multi-wavelength pump source can be used; a composite light beam can be output. When the gain fiber and fiber laser proposed in the present application are applied in the field of laser processing, the composite light beam has the beneficial effects of controlling the molten pool, suppressing spatter, and preheating the processed materials and welding rods.

[0006] In order to solve the above technical problems, this application proposes the following technical solutions: A gain optical fiber with low numerical aperture and high absorption flatness comprises a gain core, a step layer and a cladding with successively decreasing refractive indices. The gain optical fiber has a stable pump light absorption rate in the 900nm-1000nm band, and the step layer is used to reduce the numerical aperture of the gain core.

[0007] Optionally, the gain core has a stable pump light absorption rate in the 930nm-960nm band.

[0008] Optionally, the concentration of phosphorus doped in the gain fiber core is between 5 mol % and 20 mol %.

[0009] Optionally, the numerical aperture of the gain core is not greater than 0.11.

[0010] Optionally, the cross-sectional shape of the step layer includes a circle, a rectangle, a D-shape or an octagon.

[0011] The present application also provides a fiber laser, comprising any of the above gain fibers, and also comprising a pump source and a first-stage optical path; the pump source outputs pump light, the first-stage optical path comprises an active fiber, the active fiber comprises an active core, and the active core forms a signal light; the gain core receives the signal light, and the step layer and the cladding receive the pump light.

[0012] Optionally, the gain core is mode field matched to the active core.

[0013] Optionally, the gain core outputs a first light beam, the step layer outputs a second light beam, and the first light beam and the second light beam surrounding the first light beam form a composite light beam.

[0014] Optionally, the pump light has at least one central wavelength.

[0015] The present application also provides a laser processing device, comprising any of the above fiber lasers.

[0016] Compared with the prior art, this application has at least the following beneficial effects: The gain fiber with low numerical aperture and stable absorption rate provided by the present application has a higher absorption rate for pump light in a wider wavelength range, and the influence of the central wavelength fluctuation of the pump light on the output power of the gain fiber is reduced, and the gain fiber can be pumped by pump sources with different central wavelengths, thereby improving the stability of the power output by the gain fiber; a step layer is arranged between the cladding and the gain core, thereby reducing the numerical aperture of the gain core, achieving better beam quality, increasing the power threshold of transverse mode instability, and improving the optical coupling efficiency and the stability of the transverse mode output by the gain fiber.

[0017] Using the gain fiber with low numerical aperture and stable absorption rate provided by the present application, the gain fiber core is doped with a high concentration of phosphorus, which stabilizes the gain fiber core's absorption rate of pump light in the 900nm-1000nm band, improves the stability of the power output of the gain fiber, and improves the anti-photon darkening ability of the gain fiber; the setting of the step layer reduces the numerical aperture of the gain fiber core, improves the stability of the transverse mode output by the gain fiber, and also plays a role in binding the cladding light, thereby improving the utilization rate of light energy.

[0018] The present application also provides a fiber laser, which uses the gain fiber with low numerical aperture and stable absorption rate provided by the present application, which can reduce the specification requirements on the wavelength range of the pump source output, reduce the pump source cost, and the power output of the fiber laser is more stable; a pump source with at least one central wavelength can be used, for example, a pump source with central wavelengths of 915nm and 976nm can be used to pump the gain fiber at the same time, the wavelength range of the pump light is wider, and the nonlinear threshold in the laser is improved; the absorption rate of the pump light is less affected by the wavelength change, the temperature change of the cladding light stripper is low, and the heat dissipation standard of the cladding light can be appropriately reduced, reducing Energy loss and heat dissipation cost when light energy is converted into heat energy; the gain optical fiber with low numerical aperture and stable absorption rate provided by the present application is provided with step layer bound cladding light, which reduces the stripping pressure of the cladding light stripper in the optical path, and can reduce the specification requirements for the cladding light stripper or cancel the setting of the cladding light stripper in subsequent operations; the step layer bound cladding light is located around the first light beam output by the gain fiber core, and can be used as processing auxiliary light to participate in the processing operation when the optical fiber laser is applied to laser processing, thereby improving the utilization rate of light energy, making the temperature field of the processing surface smoother, and playing a role in controlling the molten pool, suppressing spatter, and preheating the processing material and welding rod. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] One or more embodiments are exemplarily described by corresponding drawings, which do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings represent similar elements, and the figures in the drawings do not constitute proportional limitations unless otherwise stated.

[0020] Figure 1 It is a schematic diagram of the refractive index distribution and cladding structure of the gain optical fiber provided in some embodiments of the present application.

[0021] Figure 2 It is a schematic diagram showing that the absorption rate of the gain optical fiber varies with the wavelength in the prior art.

[0022] Figure 3 It is a schematic diagram showing the variation of the absorption rate of the gain optical fiber with the wavelength provided in some embodiments of the present application.

[0023] Figure 4 It is a schematic diagram of the cross-sectional shape of the step layer of the gain optical fiber provided in some embodiments of the present application.

[0024] Figure 5 It is a schematic diagram of the optical path of the gain fiber provided in some embodiments of the present application when applied in a fiber laser.

[0025] Among them, the reference numerals in the figure are: 11. active optical fiber; 21. gain optical fiber; 31. pump signal combiner; 111. active core; 101. signal light; 211. gain core; 210. step layer; 212. cladding; 200. pump light; 201. first light beam; 202. second light beam. DETAILED DESCRIPTION

[0026] The embodiments of the present application are further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the embodiments of the present application, rather than to limit the embodiments of the present application. It should also be noted that, for ease of description, only parts related to the embodiments of the present application are shown in the accompanying drawings, rather than all structures.

[0027] In addition, the terms first, second, third, etc. in the specification and claims are only used for the purpose of describing the same technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated, nor necessarily describing the order or time sequence. The terms are interchangeable where appropriate. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features.

[0028] Similarly, the terms "fixed" and "connected" used in the specification and claims should not be construed as limited to direct connection. Therefore, the expression "device A is connected to device B" should not be limited to a device or system in which device A is directly connected to device B, but means that there is a path between device A and device B, which may be a path including other devices or tools.

[0029] In the prior art, the gain fiber has a band with low absorption rate in the 900nm-1000nm band. For example, when the output wavelength of the pump light fluctuates to the low absorption rate band of the gain fiber, the gain fiber cannot completely absorb the pump light, which will cause a large amount of pump light to leak out, waste light energy, form a heat source, and seriously endanger the safety of the equipment.

[0030] The present application proposes a gain optical fiber 21 with low numerical aperture and stable absorption rate, such as Figure 1As shown, it includes a gain core 211, a step layer 210 and a cladding 212 with successively decreasing refractive indices, wherein the gain core 211 has the highest refractive index, the step layer 210 has a refractive index less than the gain core 211, and the step layer 210 has a refractive index greater than the cladding 212; the gain fiber 21 proposed in the present application has a stable pump light absorption rate in the 900nm-1000nm band, and has low requirements for the wavelength stability of the pump light. The gain fiber 21 proposed in the present application is provided with a step layer 210, and a low numerical aperture structure is formed between the step layer 210 and the gain core 211, which is used to reduce the numerical aperture of the gain core 211. Those skilled in the art will know that the numerical aperture of the gain core 211 is jointly determined by the refractive index of the gain core 211 itself and the refractive index of the material surrounding the gain core 211, and the formula is: Since the refractive index of the step layer 210 is between the gain core 211 and the cladding 212, the numerical aperture between the gain core 211 and the step layer 210 is smaller than the numerical aperture between the gain core and the cladding of the same refractive index without the step layer.

[0031] Compared with the prior art, this application has at least the following beneficial effects: The gain fiber with low numerical aperture and stable absorption rate provided by the present application has a higher absorption rate for pump light in a wider wavelength range, and the influence of the central wavelength fluctuation of the pump light on the output power of the gain fiber is reduced, thereby improving the stability of the power output by the gain fiber; a step layer is arranged between the cladding and the gain core, thereby reducing the numerical aperture of the gain core, achieving better beam quality, increasing the power threshold of transverse mode instability, and improving the optical coupling efficiency and the stability of the transverse mode output by the gain fiber.

[0032] In some embodiments proposed in the present application, the schematic diagram of the variation of the absorption rate of the gain optical fiber 21 proposed in the present application with the wavelength is as follows: Figure 3 As shown, Figure 3 The horizontal axis is the wavelength, and the vertical axis is the absorption rate, wherein the vertical axis is only a relative reference and does not contain a specific numerical meaning. Optionally, the gain core has a stable pump light absorption rate in the 930nm-960nm band. Those skilled in the art will know that the absorption rate of the prior art gain fiber varies with wavelength. Figure 2 As shown, Figure 2 The horizontal axis is the wavelength, and the vertical axis is the absorbance. The vertical axis is only a relative reference and does not contain a specific numerical meaning. Figure 2 It can be seen that the gain fiber of the prior art has two absorption peaks in the central wavelength band of 915nm and 976nm, and the absorption rate decreases rapidly in the band of 930nm-960nm. Figure 3As shown, the gain fiber 21 proposed in the present application has a stable pump light absorption rate in the 930nm-960nm band, which can reduce the absorption rate change of the gain fiber 21 caused by the wavelength change of the pump light, improve the utilization rate of the pump light and the stability of the light output of the gain fiber 21, reduce the requirements for the wavelength range of the pump light, and reduce the utilization cost of the gain fiber 21.

[0033] The gain fiber 21 has a stable high pump light absorption rate in the third band with a central wavelength of 976nm±15nm. Figure 2 It can be seen that the gain fiber of the prior art has an extremely narrow absorption peak in the central wavelength band of 976nm, and the slope of the absorption rate changing with wavelength is extremely large. In order to adapt to the extremely narrow absorption peak of the gain fiber in the 976nm band, technicians in this field have developed a pump source locking technology and controlled the pump source to work in an extremely narrow temperature range. Figure 3 It can be known that in some embodiments, the gain fiber 21 provided in the present application has a stable high pump light absorption rate in the third band with a central wavelength of 976nm±15nm. When the gain fiber 21 is pumped by a pump source with a central wavelength of 976nm, the drift of the central wavelength has little effect on the absorption rate of the pump light, which can reduce the requirements for the wavelength range of the pump light, improve the utilization rate of light energy, and reduce the use cost of the gain fiber 21. The drift of the central wavelength has little effect on the absorption rate of the pump light, and the length of the gain fiber 21 can be reasonably estimated and controlled within a suitable range, avoiding the increase in cost, deterioration of beam quality and reduction of nonlinear benefit threshold caused by the excessive length of the gain fiber 21; at the same time, avoiding the pump light that cannot be completely absorbed due to the excessively short length of the gain fiber 21, and a large amount of pump light remains in the cladding and becomes heat energy, increasing the heat dissipation pressure of the laser.

[0034] Optionally, the gain fiber 21 is doped with a high concentration of phosphorus, and in particular, the concentration of phosphorus doped in the gain fiber core 211 is between 5 mol% and 20 mol%. Figure 3 It can be seen that in some embodiments, the curve of the absorptivity of the gain fiber 21 provided in the present application changing with wavelength has the beneficial effect of stabilizing the absorptivity, and some technical solutions for achieving this beneficial effect are to dope a high concentration of phosphorus in the gain core 211. Doping with a high concentration of phosphorus can not only change the curve of the absorptivity of the gain fiber 21 changing with wavelength, so that it has a stable absorptivity in the 900nm-1000nm band, but also has the beneficial effect of improving the anti-photon darkening of the gain fiber 21.

[0035] Optionally, the numerical aperture between the gain core 211 and the step layer 210 is not greater than 0.11. There are already some phosphorus-doped gain fibers on the market, which have a relatively stable absorption rate for pump light with a wavelength in the 915nm-970nm band. However, phosphorus doping will cause the core refractive index to increase, resulting in its numerical aperture cannot be effectively reduced. The numerical aperture of the existing optical fiber on the market that has a relatively stable absorption rate for pump light with a wavelength in the 915nm-970nm band is 0.11. In some embodiments of the present application, a low numerical aperture structure is formed between the gain core 211 and the step layer 210, which reduces the numerical aperture of the gain core 211, so that the numerical aperture between the gain core 211 and the step layer 210 provided in the present application is not greater than 0.11. The low numerical aperture structure is formed between the gain core 211 and the step layer 210 provided in the present application, which increases the transverse mode instability threshold of the gain fiber 21 and improves the beam quality of the light beam output by the gain fiber 21.

[0036] Alternatively, if Figure 4 As shown, the cross-sectional shape of the step layer 210 includes a rectangle, a D shape or an octagon. The setting of the step layer 210 can not only reduce the numerical aperture of the gain core 211 and increase the transverse mode instability threshold of the gain fiber 21, but also can bind the cladding light and increase the probability of the cladding light entering the gain core 211 and being absorbed. Preferably, the cross-sectional shape of the step layer 210 is set to increase the ability of the step layer 210 to bind the cladding light. In some embodiments provided in the present application, such as Figure 4 As shown, the cross-sectional shape of the step layer 210 includes a rectangle, a D shape or an octagon. In some embodiments of the present application, the cross-sectional shape of the step layer 210 is set to a shape other than a circle, which can reduce the formation of spiral light in the cladding 212 and increase the binding ability of the step layer 210 to the cladding light. Preferably, when the cladding light bound by the step layer 210 is used as auxiliary light for processing, the cross-sectional shape of the step layer 210 will give the auxiliary light a specific spot shape to assist the processing process.

[0037] This application also provides some fiber lasers, whose optical paths are as follows Figure 5 As shown, it includes any of the gain fibers 21 as described above, and also includes a pump source and a first-stage optical path; the pump source outputs pump light 200, and the first-stage optical path includes an active fiber 11, and the active fiber 11 includes an active core 111, and the active core 111 forms a signal light 101; the gain core 211 receives the signal light 101, and the step layer 210 and the cladding 212 receive the pump light 200 emitted by the pump source. In some embodiments, the gain fiber 21 provided in the present application is provided in a fiber laser as part of an optical amplifier. When the gain fiber 21 provided in the present application is provided in a fiber laser as part of an optical amplifier, as shown in FIG. Figure 5As shown, the signal light 101 is outputted by the active optical fiber 11 , and is transmitted into the gain core 211 after passing through the pump signal combiner 31 .

[0038] In some preferred embodiments of the present application, the gain core 211 is mode-field matched with the active core 111, and the pump signal combiner 31 can use end-face pumping or side-face pumping. The gain core 211 is mode-field matched with the active core 111 to prevent the beam quality of the signal light 101 output by the active core 111 from deteriorating, and improve the beam quality of the first light beam 201 output by the gain core 211. In particular, the core diameter of the gain core 211 and the core diameter of the active core 111 are both between 10 μm and 20 μm; the numerical aperture between the step layer 210 and the gain core 211 and the numerical aperture of the active core 111 are both between 0.06 and 0.11. Those skilled in the art will know that the more mature technologies in the market generally use active optical fibers with a specification size of 14 / 250 and a numerical aperture of 0.065 to output signal light 101. Some preferred embodiments of the present application set the specification size and numerical aperture of the gain optical fiber 21 to be not much different from those of the active optical fiber 11, so as to better achieve mode field matching between the gain core 211 and the active core 111.

[0039] Optionally, the gain core 211 outputs a first light beam 201, the step layer 210 outputs a second light beam 202, and the first light beam 201 and the second light beam 202 surrounding the first light beam form a composite light beam. Figure 5 As shown, the pump light 200 is transmitted into the step layer 210 and the cladding 212 of the gain fiber 21 after passing through the pump signal combiner 31; the gain core 211 absorbs the pump light 200 and amplifies the signal light 101, outputting a first light beam 201, and the unabsorbed pump light 200 is transmitted between the cladding 212 and the step layer 210, and is bounded by the step layer 210 to form a second light beam 202 with low central intensity. The first light beam 201 and the second light beam 202 form a composite light beam, as shown in FIG. Figure 5 The relationship between the spot energy and the spot diameter is shown in the figure on the right. In some embodiments of the present application, Figure 4 As shown, the cross-sectional shape of the step layer 210 includes a circle, a rectangle, a D-shape or an octagon. When outputting the second light beam 202, the non-circular step layer 210 can output a special-shaped light beam to form auxiliary processing light with different spot shapes.

[0040] Optionally, the pump light 200 has at least one central wavelength. The gain fiber 21 provided in the present application has a stable high pump light absorption rate in the 900nm-1000nm band. In some embodiments, the wavelength range of the pump light can be selected in the 900nm-1000nm band; those skilled in the art can know that the 900nm-1000nm band covers more than one pump source with a central wavelength, and the pump source emitting the pump light can have any one or more central wavelengths in the 900nm-1000nm band. Preferably, when the pump light has multiple central wavelengths, the corresponding optical power of a single wavelength is reduced, thereby increasing the nonlinear threshold in the laser.

[0041] Preferably, the central wavelength of the pump source includes 915 nm and / or 940 nm and / or 976 nm. In some embodiments, the schematic diagram of the absorption rate of the gain fiber 21 provided in the present application varying with wavelength is as follows: Figure 3 Observation Figure 3 It can be seen that the gain fiber 21 proposed in the present application has a high pump light absorption rate in the 940nm band with a central wavelength close to that in the 915nm band, and has a stable high pump light absorption rate in the third band with a central wavelength of 976nm±15nm. Those skilled in the art can know that in the prior art, the pump source in the 900nm-1000nm band has three typical central wavelengths of 915nm, 940nm and 976nm. The first pump source with a central wavelength of 915 nm and the second pump source with a central wavelength of 976 nm have been used in the prior art. The fiber laser including the gain fiber 21 proposed in the present application can also use a second pump source with a central wavelength of 940 nm to pump the gain fiber 21, and the first pump source with a central wavelength of 915 nm, the second pump source with a central wavelength of 940 nm, and the third pump source with a central wavelength of 976 nm can be used in combination, or any two of the three pump sources can be used together, or one of the pump sources can be used, which is not a limitation of the present application.

[0042] Those skilled in the art can know that in the prior art, the pump source can include two or more central wavelengths. A first dual-wavelength pump source outputting 915nm and 976nm, a second dual-wavelength pump source outputting 915nm and 940nm, a third dual-wavelength pump source outputting 940nm and 976nm, and a triple-wavelength pump source outputting 915nm, 940nm and 976nm, at least one of which can also be independently or jointly arranged in the fiber laser provided in the present application as the pump source of the gain fiber 21 provided in the present application. Pumping the gain fiber 21 with multi-band pump light can increase the nonlinear threshold in the laser.

[0043] Optionally, the fiber laser further includes a passive optical waveguide, which is adapted to the output end of the gain fiber 21. The output beam of the gain fiber 21 provided in the present application can be used as the output beam of the fiber laser, and the cladding light bound by the step layer 210 can be used as the processing auxiliary light output by the fiber laser. In some embodiments, a passive optical waveguide is provided at the output end of the gain fiber 21 to transmit the output beam of the gain fiber 21 while protecting the gain fiber 21. The passive optical waveguide is connected to the output end of the gain fiber 21 by direct fusion, taper fusion or coupling connection, and is used to receive the composite light beam output by the gain fiber 21; the number of claddings of the passive optical waveguide is equal to or greater than the number of claddings at the output end of the gain fiber 21, so as to maintain the spot energy distribution of the composite light beam output by the gain fiber 21, play the expected effect of the cladding design of the gain fiber 21, and reduce the generation of stray light; the maximum cladding diameter of the passive optical waveguide is equal to or greater than the maximum cladding diameter of the output end of the gain fiber 21, and all the composite light beams output by the gain fiber 21 are collected in the passive optical waveguide and transmitted, thereby reducing the waste of light energy.

[0044] The present application also provides a laser processing device, including any of the above fiber lasers. In some embodiments, the composite light beam output by the fiber laser provided in the present application is used as a processing light beam in the laser processing device provided in the present application; it is understandable that focusing the composite light beam output by the fiber laser provided in the present application, collimating it, and then acting on the processing material is also within the scope of the present application.

[0045] Compared with the prior art, this application has at least the following beneficial effects: The gain fiber with low numerical aperture and stable absorption rate provided by the present application has a higher absorption rate for pump light in a wider wavelength range, and the influence of the central wavelength fluctuation of the pump light on the output power of the gain fiber is reduced, and the gain fiber can be pumped by pump sources with different central wavelengths, thereby improving the stability of the power output by the gain fiber; a step layer is arranged between the cladding and the gain core, thereby reducing the numerical aperture of the gain core, achieving better beam quality, increasing the power threshold of transverse mode instability, and improving the optical coupling efficiency and the stability of the transverse mode output by the gain fiber.

[0046] Using the gain fiber with low numerical aperture and stable absorption rate provided by the present application, the gain fiber core is doped with a high concentration of phosphorus, which stabilizes the gain fiber core's absorption rate of pump light in the 900nm-1000nm band, improves the stability of the power output of the gain fiber, and improves the anti-photon darkening ability of the gain fiber; the setting of the step layer reduces the numerical aperture of the gain fiber core, improves the stability of the transverse mode output by the gain fiber, and also plays a role in binding the cladding light, thereby improving the utilization rate of light energy.

[0047] The present application also provides a fiber laser, which uses the gain fiber with low numerical aperture and stable absorption rate provided by the present application, which can reduce the specification requirements on the wavelength range of the pump source output, reduce the pump source cost, and the power output of the fiber laser is more stable; a pump source with at least one central wavelength can be used, for example, a pump source with central wavelengths of 915nm, 940nm and 976nm can be used to pump the gain fiber at the same time, the wavelength range of the pump light is wider, and the nonlinear threshold in the laser is improved; the absorption rate of the pump light is less affected by the wavelength change, the temperature change of the cladding light stripper is low, and the heat dissipation standard of the cladding light can be appropriately reduced. , reducing the energy loss and heat dissipation cost of converting light energy into heat energy; the step layer bound cladding light is set in the gain optical fiber with low numerical aperture and stable absorption rate provided by the present application, which reduces the stripping pressure of the cladding light stripper in the optical path, and can reduce the specification requirements for the cladding light stripper or cancel the setting of the cladding light stripper in subsequent operations; the step layer bound cladding light is located around the first light beam output by the gain fiber core, and in the process of applying the optical fiber laser to laser processing, it can be used as processing auxiliary light to participate in the processing operation, improve the utilization rate of light energy, make the temperature field of the processing surface smoother, and play a role in controlling the molten pool, suppressing spatter, and preheating the processing material and welding rod.

[0048] In summary, the gain fiber provided by the present application is used in a fiber laser, and the gain core has good anti-photon darkening ability and pump light absorption flatness, which can reduce the temperature control of the pump source, use a pump source with a larger light output wavelength range, and use a pump source with a different central wavelength, which reduces the production and maintenance costs of the pump source, improves the nonlinear threshold in the laser, and the light output power is less affected by the wavelength fluctuation range, and has a stable output light power; the setting of the step layer can obtain output light with high beam quality, reduce the instability threshold of the transverse mode, and output a high-quality beam with a stable transverse mode. The setting of the step layer can bind the cladding light for processing assistance, which can reduce the use specifications of the cladding light stripper, or not set the cladding light stripper, thereby improving the utilization rate of light energy. Fiber lasers are applied to the field of laser processing, and the bound cladding light is used as processing auxiliary light, which can improve processing efficiency, control the molten pool, preheat the processing material, preheat the welding rod, and improve the processing effect. Therefore, the present invention effectively overcomes the various shortcomings in the prior art and has a high industrial utilization value.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Under the concept of the present application, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other changes in different aspects of the present application as described above, which are not provided in detail for the sake of simplicity. Although the present application has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that the technical solutions described in the aforementioned embodiments can still be modified, or some of the technical features can be replaced by equivalents. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A gain optical fiber with low numerical aperture and stable absorption rate, characterized in that: The optical fiber comprises a gain core, a step layer and a cladding with successively decreasing refractive indices. The gain optical fiber has a stable pump light absorption rate in the 900nm-1000nm band, and the step layer and the gain core form a low numerical aperture structure.

2. The gain optical fiber according to claim 1, characterized in that: The gain fiber core has a stable pump light absorption rate in the 930nm-960nm band.

3. The gain optical fiber according to claim 1, characterized in that: The concentration of phosphorus doped in the gain fiber core is between 5 mol% and 20 mol%.

4. The gain optical fiber according to claim 1, characterized in that: The numerical aperture of the gain core is no greater than 0.

11.

5. The gain optical fiber according to claim 1, characterized in that: The cross-sectional shape of the step layer includes a circle, a rectangle, a D-shape or an octagon.

6. A fiber laser, characterized in that: The gain optical fiber comprises the gain optical fiber according to any one of claims 1 to 5, further comprising a pump source and a first-stage optical path, wherein the pump source outputs pump light, the first-stage optical path comprises an active optical fiber, the active optical fiber comprises an active core, and the active core forms a signal light; the gain core receives the signal light, and the step layer and the cladding receive the pump light.

7. The optical fiber laser according to claim 6, characterized in that: The gain core and the active core are mode-field matched.

8. The optical fiber laser according to claim 6, characterized in that: The gain core outputs a first light beam, the step layer outputs a second light beam, and the first light beam and the second light beam surrounding the first light beam form a composite light beam.

9. The optical fiber laser according to claim 6, characterized in that: The pump light has at least one central wavelength.

10. A laser processing device, characterized in that: Comprising the fiber laser as described in claims 6-9.

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