CN111817119B - Fiber laser with fiber core Raman return light resisting function - Google Patents
Fiber laser with fiber core Raman return light resisting function Download PDFInfo
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- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
- H01S3/0078—Frequency filtering
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- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
- H01S3/0064—Anti-reflection devices, e.g. optical isolaters
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- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/06—Construction or shape of active medium
- H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
- H01S3/067—Fibre lasers
- H01S3/06708—Constructional details of the fibre, e.g. compositions, cross-section, shape or tapering
- H01S3/06729—Peculiar transverse fibre profile
- H01S3/06733—Fibre having more than one cladding
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/06—Construction or shape of active medium
- H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
- H01S3/067—Fibre lasers
- H01S3/0675—Resonators including a grating structure, e.g. distributed Bragg reflectors [DBR] or distributed feedback [DFB] fibre lasers
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Abstract
The invention discloses an optical fiber laser with a fiber core Raman return light resisting function, which comprises an indicating laser, a first Raman isolation unit, an optical fiber oscillator resonant cavity, a second Raman isolation unit and QBH output optical fibers which are connected in sequence, wherein the first Raman isolation unit comprises a first Raman tilt grating, the second Raman isolation unit comprises a second Raman tilt grating, the long period end of the first Raman tilt grating points to the input optical fibers of the optical fiber oscillator resonant cavity, and the long period end of the second Raman tilt grating points to the output optical fibers of the optical fiber oscillator resonant cavity. The fiber laser designed by the invention can filter the externally generated fiber core Raman return light before entering the fiber oscillator resonant cavity, effectively avoids the damage of the fiber core Raman return light to the fiber laser, achieves the effects of protecting devices inside the laser and stabilizing the output power of the laser in the process of processing materials, and is particularly suitable for the industrial laser processing of high-reflectivity materials.
Description
Technical Field
The invention belongs to the technical field of laser, relates to a fiber laser, and particularly relates to a fiber laser with a fiber core Raman return light resisting function.
Background
The fiber laser has the advantages of high efficiency, high beam quality, high compactness and the like, and is widely applied to the modern high-tech industrial processing technology. At present, high-power multimode laser is mainly adopted for processing industrial materials. Compared with multimode fiber lasers, high-power single-mode fiber lasers have higher beam quality and have greater advantages in some material processing applications requiring extremely high brightness, such as remote processing, fine processing and processing of high-reflectivity materials (copper, aluminum, etc.), and therefore, the applicant is dedicated to research and development in this new field.
During the research of high-power single-mode fiber laser processing, the applicant finds that the application of high-power single-mode fiber laser to material processing faces a new challenge, namely that reflected light generated on the surface of the material enters the output fiber of the single-mode fiber laser from the output end cap. These reflected lights can be further divided into two components: (1) reflected light (hereinafter referred to as cladding return light) entering the fiber laser and outputting the cladding of the optical fiber; (2) the reflected light entering the fiber core of the output optical fiber (hereinafter referred to as fiber core return light, including signal light band fiber core return light and fiber core raman return light). The cladding return light can be filtered by a traditional cladding light filter, so that the influence of the cladding return light on the single-mode fiber laser is small. The power of the return light of the fiber core of the signal light wave band is far lower than the power of the output laser, so that the laser gain competition process in the resonant cavity cannot be influenced, and the influence on the laser can be ignored. Fiber core raman echo is when passing through QBH output fiber (the optic fibre of taking laser output end cap promptly, conventional device, QBH is the quartz bulk head entirely, laser output end cap promptly) and fiber laser resonant cavity, and the laser power that QBH outputs in optic fibre and the resonant cavity can be because stimulated raman scattering effect converts into fiber core raman echo, leads to output laser power to reduce, and the promotion of fiber core raman echo optical power, and too strong fiber core raman echo then can lead to the damage of laser instrument internal device. Therefore, how to avoid the damage of the high-power single-mode fiber laser by the fiber core raman echo is an important challenge for the high-power single-mode fiber laser to be used for material processing.
The fiber core Raman return light is formed by reflecting the Raman light in the output laser by the processing material, so that the fiber core Raman return light can be effectively inhibited by reducing the Raman light power in the output laser. Although in the prior art, chinese patent publication No. CN109217098A discloses a method for suppressing stimulated raman scattering effect in a high power fiber oscillator, which is characterized in that a raman light tilt grating is added inside a resonant cavity of the fiber oscillator to filter raman light generated inside the fiber oscillator, reduce the raman light generated inside the oscillator, and further reduce the raman light in the output laser. However, the technology disclosed in this patent document is only applicable to application scenarios that do not require long-distance QBH output fibers, such as directional energy weapon systems (laser is applied to a long-distance target, and return light is negligible), but is not applicable to high-power laser industrial processing that requires long-distance QBH output fibers. The Raman light in the output laser of the high-power single-mode industrial laser provided with the long-distance QBH output fiber comes from two sources, namely a fiber oscillator and the QBH output fiber. The former is Raman laser generated when the signal light power in the high-power fiber oscillator cavity exceeds the stimulated Raman scattering effect threshold, and the latter is generated when the high-power laser is transmitted in a long distance in the QBH transmission fiber to trigger the stimulated Raman scattering effect and output laser is converted into Raman light. Therefore, the technology in patent document CN109217098A cannot reduce the raman light generated in the QBH output fiber, and this part of raman light can also be reflected by the end face of the material, converted into core raman return light, and returned to the inside of the high-power fiber laser, thereby causing damage to the internal devices of the laser.
The chinese patent document CN108054624B applied by the applicant provides an optical fiber laser with the function of resisting fiber core reflected light, which is characterized in that backward pumping is adopted to reduce the raman light generated inside the oscillator, and further reduce the raman light in the output laser, so as to achieve the purpose of reducing fiber core raman return light; and then, by reducing the reverse transmission insertion loss and mismatch fusion of the beam combiner, the fiber core Raman return light is ensured to smoothly pass through the pumping signal beam combiner, and then is coupled to the inner cladding through the mismatch fusion, and is filtered by the cladding light filter, so that the purpose of protecting the indicating light source is achieved. The method avoids the damage of the laser caused by the Raman return light of the fiber core from the two aspects of inhibiting the generation of the Raman light and leading the Raman light. However, the fiber core raman echo still passes through the gain fiber in the fiber oscillator resonant cavity, which causes the output laser power to be converted into the fiber core raman echo power due to the stimulated raman scattering effect, and further causes the laser power to be unstable, so that the material processing effect fluctuates.
In summary, industrial processing of high power single mode fiber lasers is still an emerging field, and a large amount of development and research is needed.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides the optical fiber laser with the function of fiber core Raman return light resistance. The fiber laser designed by the invention can realize safe operation and stable output power of the laser under the condition of stronger fiber core Raman return power, realizes stable material processing effect and is more suitable for laser processing of high-reflectivity materials.
In order to solve the technical problems, the invention adopts the following technical scheme.
The utility model provides a fiber laser with anti fibre core raman echo function, keeps apart unit and QBH output fiber including instruction laser, first raman that connect gradually, fiber oscillator resonant cavity, second raman, first raman keeps apart the unit and includes first raman tilt grating, second raman keeps apart the unit and includes second raman tilt grating, the long period end of first raman tilt grating is directional the input fiber of fiber oscillator resonant cavity, the long period end of second raman tilt grating is directional the output fiber of fiber oscillator resonant cavity.
In the fiber laser with the function of resisting core raman echo, preferably, the first raman isolation unit further includes a first double-clad fiber, the first raman tilt grating is written in a core of the first double-clad fiber, and the first raman tilt grating is a chirped double-clad fiber grating; the second Raman isolation unit further comprises a second double-clad fiber, the second Raman tilt grating is inscribed in the fiber core of the second double-clad fiber, and the second Raman tilt grating is a chirped double-clad fiber grating.
Preferably, in the fiber laser with the function of fiber core raman returning light resistance, the first raman tilt grating reflects the first fiber core raman returning light transmitted from the indicator laser to the fiber oscillator resonant cavity into the inner cladding of the first double-clad fiber, the central wavelength of the first raman tilt grating is equal to the central wavelength of the first-order stimulated raman scattering light of the signal light of the fiber oscillator resonant cavity, the reflectivity of the first raman tilt grating is greater than 99%, and the 3dB bandwidth is greater than or equal to 5 nm.
In the fiber laser with the function of fiber core raman return light resistance, preferably, the second raman tilt grating reflects the second fiber core raman return light transmitted by the QBH output fiber to the fiber oscillator resonant cavity into the inner cladding of the second double-clad fiber, the central wavelength of the second raman tilt grating is equal to the central wavelength of the first-order stimulated raman scattering light of the signal light of the fiber oscillator resonant cavity, the reflectivity of the second raman tilt grating is greater than 99%, and the 3dB bandwidth is greater than or equal to 5 nm.
Preferably, the input fiber of the fiber oscillator resonant cavity is a third double-clad fiber, the third double-clad fiber and the first double-clad fiber are respectively and correspondingly equal in fiber core diameter, fiber core numerical aperture, inner cladding outer diameter and inner cladding numerical aperture, the fiber core diameter is 10 μm to 20 μm, the fiber core numerical aperture is 0.06 μm to 0.075, the inner cladding outer diameter is 250 μm to 400 μm, and the inner cladding numerical aperture is 0.44 μm to 0.46. That is, the core diameters of the third double-clad fiber and the first double-clad fiber are equal, the core numerical apertures of the third double-clad fiber and the first double-clad fiber are equal, the inner cladding outer diameters of the third double-clad fiber and the first double-clad fiber are equal, and the inner cladding numerical apertures of the third double-clad fiber and the first double-clad fiber are equal.
The above-mentioned fiber laser with anti-fiber core raman echo function, it is preferred, the output fiber of fiber oscillator resonant cavity is fourth double-clad fiber, QBH output fiber is fifth double-clad fiber, fourth double-clad fiber, second double-clad fiber and fifth double-clad fiber correspond on fiber core diameter, fiber core numerical aperture, inner cladding external diameter, inner cladding numerical aperture respectively and equal, the fiber core diameter is 20 mu m ~ 30 mu m, fiber core numerical aperture is 0.06 ~ 0.075, the inner cladding external diameter is 250 mu m ~ 400 mu m, inner cladding numerical aperture is 0.44 ~ 0.46. That is, the core diameters of the fourth double-clad fiber, the second double-clad fiber and the fifth double-clad fiber are equal, the core numerical apertures of the fourth double-clad fiber, the second double-clad fiber and the fifth double-clad fiber are equal, the inner cladding outer diameters of the fourth double-clad fiber, the second double-clad fiber and the fifth double-clad fiber are equal, and the inner cladding numerical apertures of the fourth double-clad fiber, the second double-clad fiber and the fifth double-clad fiber are equal.
Preferably, the output fiber of the indication laser is a single-mode fiber, the diameter of the fiber core in the single-mode fiber is 4-6 μm, the numerical aperture of the fiber core is 0.08-0.12, the diameter of the cladding is 125 μm, and the output fiber of the indication laser and the first raman isolation unit are welded in a mode of aligning the axis of the fiber core.
Preferably, the central wavelength of the indicating laser output by the indicating laser is 635nm, and the indicating laser sequentially passes through the first raman isolation unit, the fiber oscillator resonant cavity, the second raman isolation unit and the QBH output fiber along the fiber core of the optical fiber output by the indicating laser and is output.
Preferably, the application scenario of the fiber laser with the anti-fiber core raman echo function is industrial laser processing, but is not limited thereto.
Preferably, the industrial laser processing includes laser cutting, laser welding or laser cladding, and the industrial laser processing is suitable for laser processing of a high-reflectivity metal material, and the high-reflectivity metal material includes one or more of red copper, aluminum alloy and silver.
When the raman isolation unit (the first raman isolation unit or the second raman isolation unit) is manufactured, a raman tilt grating can be inscribed on one double-clad fiber to form the raman isolation unit, or a plurality of double-clad fibers and the double-clad fiber with the raman tilt grating are connected in series and welded to form the raman isolation unit, namely, as long as the raman isolation unit is formed by the double-clad fibers and the raman tilt grating according to the design requirements of the invention, the raman isolation unit belongs to the scope defined by the raman isolation unit of the invention and is not limited by the manufacturing method of the raman isolation unit.
In the invention, Raman light generated inside the fiber oscillator resonant cavity comprises forward transmission Raman light (transmitted to the QBH output fiber) and backward transmission Raman light (transmitted to the indicating laser), wherein the backward transmission Raman light forms first fiber core Raman return light after being reflected inside the indicating laser, and the forward transmission Raman light forms second fiber core Raman return light after being reflected on the surface of a processing workpiece.
The main innovation points of the invention are as follows:
the Raman return light generated by the high-power laser during processing materials can damage the optical fiber oscillator, mainly reflected in that the power is reduced, the beam quality is deteriorated, the grating is damaged, and the gain optical fiber is damaged. The applicant researches and discovers that the oscillator can normally and stably work as long as Raman return light does not enter the oscillator, and even under the condition that certain proportion of Raman light exists in output light of the oscillator, the oscillator can still normally work as long as no Raman return light returns to the oscillator. Therefore, the Raman light tilt grating is added outside the laser cavity, the long-period end of the Raman light tilt grating is connected with the optical fiber oscillator, fiber core Raman return light generated outside is filtered, and the fiber core Raman return light is prevented from entering the optical fiber oscillator.
Compared with the prior art, the invention has the advantages that:
according to the invention, the first Raman isolation unit and the second Raman isolation unit are respectively welded on the outer side of the fiber oscillator resonant cavity and are welded with the long-period end according to a specific arrangement sequence, so that the fiber core Raman return light generated from the outside is filtered before entering the fiber oscillator resonant cavity, the fiber oscillator resonant cavity is prevented from being damaged by the fiber core Raman return light generated from the outside, and the effect of protecting the internal device of the laser and the output power of the laser to be stable in the process of processing materials is achieved. The fiber laser designed by the invention can effectively avoid the damage of the fiber core Raman return fiber to the fiber laser, has stable output power and is more suitable for the industrial processing of high-reflectivity materials.
The application scene of the invention is obviously different from the prior art, the invention can be applied to higher-end laser industrial processing, and can solve the problems of laser damage and unstable output power caused by over-strong fiber core Raman return light aiming at the application scene which can generate strong fiber core Raman return light, such as high-reflectivity metal materials of red copper, aluminum alloy and the like. However, the prior art (for example, CN109217098A) can only be used in the field of directional energy weapons, and the basic idea is to add a raman tilt grating inside the resonator of the oscillator to reduce the raman light generated in the fiber oscillator, thereby reducing the raman light in the output laser.
In a laser processing scenario, a high-power fiber oscillator generally needs to be equipped with a longer QBH output fiber so as to transmit high-power laser light to the surface of a processed workpiece, thereby achieving large-format laser processing, and therefore raman light in the output laser light may come from the high-power fiber oscillator and the QBH output fiber. If the prior art is adopted, only the suppression of the Raman light generated in the high-power fiber oscillator can be realized, but the Raman light generated in the longer QBH output fiber cannot be suppressed, and the part of the Raman light can be reflected back to the QBH output fiber when the high-reflectivity material is processed to form fiber core Raman return light, so that the problems of laser damage, unstable output power and the like caused by excessively strong fiber core Raman return light in the processing process of the high-reflectivity metal material cannot be solved in the prior art. Different from the prior art, the method filters the fiber core Raman return light from two ends by adding the Raman tilt grating outside the fiber oscillator resonant cavity and connecting the long period end of the Raman tilt grating with the fiber oscillator resonant cavity, so that the externally generated fiber core Raman return light is filtered before entering the fiber oscillator resonant cavity, and the effect of protecting the internal devices of the laser and the output power of the laser to be stable in the process of processing materials is achieved.
Drawings
Fig. 1 is a schematic structural diagram (which is also a working schematic diagram) of an optical fiber laser having a function of preventing core raman echo in embodiment 1 of the present invention.
Fig. 2 is a schematic structural diagram (which is also a working schematic diagram) of a first raman isolation unit in embodiment 1 of the present invention.
Fig. 3 is a schematic structural diagram (which is also a working schematic diagram) of a second raman isolation unit in embodiment 1 of the present invention.
Fig. 4 is a monitoring diagram of the output laser and the core return optical power of the optical fiber laser adopting the prior art solution CN109217098A in the laser processing process.
Fig. 5 is a monitoring chart of output laser and fiber core return power of the fiber laser in the laser processing process in the embodiment 1 of the present invention.
Illustration of the drawings:
1. an indicator laser; 2. a first Raman isolation unit; 21. a first Raman tilted grating; 22. a first core; 23. a first inner cladding layer; 3. a fiber oscillator resonant cavity; 31. a first input optical fiber; 32. a first output optical fiber; 4. a second Raman isolation unit; 41. a second Raman-tilted grating; 42. a second core; 43. a second inner cladding layer; 5. QBH output fiber; 6. outputting laser; 71. raman return light of the first fiber core; 72. raman return light of the second fiber core; 81. a first reflected light; 82. the second reflected light.
Detailed Description
The invention is further described below with reference to the drawings and specific preferred embodiments of the description, without thereby limiting the scope of protection of the invention.
The materials and equipment used in the following examples are commercially available.
Example 1:
an optical fiber laser with a fiber core Raman return light resisting function is shown in fig. 1 and comprises an indicating laser 1, a first Raman isolation unit 2, a fiber oscillator resonant cavity 3, a second Raman isolation unit 4 and a QBH output fiber 5 which are sequentially connected (preferably welded). The first raman isolation unit 2 includes a first raman tilt grating 21, the second raman isolation unit 4 includes a second raman tilt grating 41, the long period end of the first raman tilt grating 21 faces the input fiber of the fiber oscillator cavity 3, the input fiber of the fiber oscillator cavity 3 is the first input fiber 31, the long period end of the second raman tilt grating 41 faces the output fiber of the fiber oscillator cavity 3, and the output fiber of the fiber oscillator cavity 3 is the first output fiber 32. The direction of laser transmission is transmitted from the indicator laser 1 in the direction of the QBH output fibre 5.
In this embodiment, a schematic structural diagram and an operation principle of the first raman isolation unit 2 are shown in fig. 2, the first raman isolation unit 2 is composed of a first double-clad fiber and a first raman tilt grating 21, the first raman tilt grating 21 is inscribed in a fiber core of the first double-clad fiber, the first raman tilt grating 21 is a chirped double-clad fiber grating, and the fiber core of the first double-clad fiber is a first fiber core 22. The left side of the first raman tilt grating 21 is a short period end pointing to the output fiber of the pointing laser 1, and the right side is a long period end pointing to the input fiber of the fiber laser resonator 3. The first core raman return light 71 transmitted from the indicator laser 1 to the fiber oscillator cavity 3 enters the first raman isolation unit 2 from the short-period end direction of the first raman tilt grating 21 along the core of the first double-clad fiber, and is coupled into the first reflected light 81 by the first raman tilt grating 21, and the first reflected light 81 is transmitted in the inner cladding of the first double-clad fiber, i.e., the first inner cladding 23, which is opposite to the first core raman return light 71. In this embodiment, the reflectivity of the first raman tilt grating 21 is greater than 99%, and the 3dB bandwidth is greater than or equal to 5 nm.
In this embodiment, a structural schematic diagram and a working principle of the second raman isolation unit 4 are shown in fig. 3, the second raman isolation unit 4 is composed of a second double-clad fiber and a second raman tilt grating 41, the second raman tilt grating 41 is inscribed in a core of the second double-clad fiber, the core of the second double-clad fiber is a second core 42, and the second raman tilt grating 41 is a chirped double-clad fiber grating. The left side of the second raman tilt grating 41 is a long period end pointing to the output fiber of the fiber oscillator resonator 3, and the right side is a short period end pointing to the QBH output fiber 5. The high-power output laser 6 generated by the fiber oscillator resonant cavity 3 passes through the second Raman isolation unit 4 along the fiber core of the second double-clad fiber and is finally output from the QBH output fiber 5. The second core raman return light 72 transmitted from the QBH output fiber 5 to the fiber oscillator cavity 3 enters the second raman isolation unit 4 from the short-period end direction of the second raman tilt grating 41 along the core of the second double-clad fiber, and is coupled into the second reflected light 82 by the second raman tilt grating 41, the second reflected light 82 is transmitted in the inner cladding of the second double-clad fiber, which is the second inner cladding 43, and the transmission direction of the second reflected light 82 is opposite to the second core raman return light 72. In this embodiment, the reflectivity of the second raman tilt grating 41 is greater than 99%, and the 3dB bandwidth is greater than or equal to 5 nm.
In this embodiment, the center wavelength of the first raman tilt grating 21 and the center wavelength of the second raman tilt grating 41 are both equal to the center wavelength of the first order stimulated raman scattered light of the signal light of the fiber oscillator resonator 3.
In this embodiment, the input fiber of the fiber oscillator resonator 3, the output fiber of the fiber oscillator resonator 3, and the QBH output fiber 5 are all double-clad fibers, and are respectively set as a third double-clad fiber, a fourth double-clad fiber, and a fifth double-clad fiber in order to distinguish them from the first double-clad fiber and the second double-clad fiber.
In this embodiment, the input fiber (third double-clad fiber) of the fiber oscillator resonator 3 and the first double-clad fiber of the first raman isolation unit 2 are respectively equal in core diameter, core numerical aperture, inner cladding outer diameter, and inner cladding numerical aperture, where the core diameter is 20 μm, the core numerical aperture is 0.065, the inner cladding outer diameter is 400 μm, and the inner cladding numerical aperture is 0.46.
In this embodiment, the output fiber (fourth double-clad fiber) of the fiber oscillator resonator 3, the second double-clad fiber of the second raman isolation unit 4, and the QBH output fiber 5 (fifth double-clad fiber) are respectively equal in the core diameter, the core numerical aperture, the inner cladding outer diameter, and the inner cladding numerical aperture, where the core diameter is 20 μm, the core numerical aperture is 0.065, the inner cladding outer diameter is 400 μm, and the inner cladding numerical aperture is 0.46.
In this embodiment, the output fiber of the indicator laser 1 is a single-mode fiber (usually, a single-clad fiber), the core diameter of the single-mode fiber is 4 μm, the core numerical aperture is 0.08, and the cladding diameter is 125 μm, and the output fiber of the indicator laser 1 and the first raman isolation unit 2 (the short-period end direction of the first raman tilt grating 21) are fused in a manner of aligning the core axes.
In this embodiment, the central wavelength of the indicating laser generated by the indicating laser 1 is 635nm, and the indicating laser sequentially passes through the first raman isolation unit 2, the fiber oscillator resonant cavity 3, the second raman isolation unit 4 and the QBH output fiber 5 along the fiber core of the output fiber of the indicating laser 1, and is finally output from the QBH output fiber 5.
The application scene of the fiber laser with the fiber core Raman echo resisting function is industrial laser processing, and is particularly suitable for the situation that strong fiber core Raman echo can be generated, such as the processing of high-reflectivity metal materials such as red copper, aluminum alloy, silver and the like.
The fiber laser of the invention can filter the first fiber core Raman return light 71 and the second fiber core Raman return light 72 from the outside of the fiber oscillator resonant cavity 3 before entering the fiber oscillator resonant cavity 3 through the first Raman isolation unit 2 and the second Raman isolation unit 4 respectively by adding the first Raman isolation unit 2 and the second Raman isolation unit 4 to the outside of the fiber oscillator resonant cavity 3, wherein the long period end of the first Raman tilt grating 21 is opposite to the input fiber of the fiber oscillator resonant cavity 3, and the long period end of the second Raman tilt grating 41 is opposite to the output fiber of the fiber oscillator resonant cavity 3, so as to ensure that the fiber core Raman return light can not enter the fiber oscillator resonant cavity 3, eliminate the influence of the fiber core Raman return light on the fiber oscillator resonant cavity 3, protect the fiber oscillator under the condition of strong fiber core Raman return light power, the stable output of the laser is kept, and the stable material processing effect is realized.
Fig. 4 shows a monitoring graph of output laser power and core reflected light power of the fiber laser adopting the CN109217098A in the prior art when processing a high-reflectivity material, which shows that when processing an aluminum alloy, the output laser generates rapid and severe power fluctuation, and the modulation depth reaches 90% (the ratio of the trough intensity to the peak intensity), while when processing a red copper material, the output laser power fluctuation is more severe, which is caused by unstable power due to the fact that the core raman return light in the core return light returns to the fiber laser resonant cavity. When the fiber laser designed by the embodiment is used for processing aluminum alloy and red copper materials, even if strong fiber core return light is generated, the output laser power of the fiber laser does not have obvious fluctuation, and the maximum modulation depth is less than 25%, as shown in fig. 5. The laser designed by the embodiment can reduce the influence of the fiber core Raman return fiber on the fiber laser, has stable output power when processing a high-reflectivity material, and can obtain better material processing effect.
The foregoing is merely a preferred embodiment of the invention and is not intended to limit the invention in any manner. Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Those skilled in the art can make many possible variations and modifications to the disclosed embodiments, or equivalent modifications, without departing from the spirit and scope of the invention, using the methods and techniques disclosed above. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments according to the technical essence of the present invention are still within the scope of the protection of the technical solution of the present invention.
Claims (5)
1. The fiber laser with the function of fiber core Raman return light resistance comprises an indicating laser (1), a first Raman isolation unit (2), a fiber oscillator resonant cavity (3), a second Raman isolation unit (4) and a QBH output fiber (5) which are sequentially connected, wherein the first Raman isolation unit (2) comprises a first Raman tilt grating (21), the second Raman isolation unit (4) comprises a second Raman tilt grating (41), the long-period end of the first Raman tilt grating (21) points to an input fiber of the fiber oscillator resonant cavity (3), and the long-period end of the second Raman tilt grating (41) points to an output fiber of the fiber oscillator resonant cavity (3);
the first Raman isolation unit (2) further comprises a first double-clad fiber, the first Raman tilt grating (21) is inscribed in the fiber core of the first double-clad fiber, and the first Raman tilt grating (21) is a chirped double-clad fiber grating; the second Raman isolation unit (4) further comprises a second double-clad fiber, the second Raman tilt grating (41) is inscribed in the fiber core of the second double-clad fiber, and the second Raman tilt grating (41) is a chirped double-clad fiber grating; the first Raman tilt grating (21) reflects first fiber core Raman return light (71) transmitted to the fiber oscillator resonant cavity (3) by the indicating laser (1) into an inner cladding of the first double-clad fiber, the central wavelength of the first Raman tilt grating (21) is equal to the central wavelength of first-order stimulated Raman scattering light of signal light of the fiber oscillator resonant cavity (3), the reflectivity of the first Raman tilt grating (21) is greater than 99%, and the 3dB bandwidth is greater than or equal to 5 nm;
the second Raman tilt grating (41) reflects second fiber core Raman return light (72) transmitted to the fiber oscillator resonant cavity (3) by the QBH output fiber (5) into an inner cladding of the second double-clad fiber, the central wavelength of the second Raman tilt grating (41) is equal to the central wavelength of first-order stimulated Raman scattering light of signal light of the fiber oscillator resonant cavity (3), the reflectivity of the second Raman tilt grating (41) is greater than 99%, and the 3dB bandwidth is greater than or equal to 5 nm;
the output optical fiber of the indicating laser (1) is a single mode optical fiber;
the application scene of the optical fiber laser with the fiber core Raman return light resisting function is industrial laser processing;
the industrial laser processing comprises laser cutting, laser welding or laser cladding, and is suitable for laser processing of high-reflectivity metal materials, wherein the high-reflectivity metal materials comprise one or more of red copper, aluminum alloy and silver.
2. The fiber laser with the function of resisting core Raman echo according to claim 1, wherein the input fiber of the fiber oscillator cavity (3) is a third double-clad fiber, the third double-clad fiber and the first double-clad fiber are respectively and correspondingly equal in core diameter, core numerical aperture, inner cladding outer diameter and inner cladding numerical aperture, the core diameter is 10 μm to 20 μm, the core numerical aperture is 0.06 to 0.075, the inner cladding outer diameter is 250 μm to 400 μm, and the inner cladding numerical aperture is 0.44 to 0.46.
3. The fiber laser with the function of resisting core Raman echo according to claim 2, wherein the output fiber of the fiber oscillator resonant cavity (3) is a fourth double-clad fiber, the QBH output fiber (5) is a fifth double-clad fiber, the fourth double-clad fiber, the second double-clad fiber and the fifth double-clad fiber are respectively and correspondingly equal in core diameter, core numerical aperture, inner cladding outer diameter and inner cladding numerical aperture, the core diameter is 20 μm to 30 μm, the core numerical aperture is 0.06 to 0.075, the inner cladding outer diameter is 250 μm to 400 μm, and the inner cladding numerical aperture is 0.44 to 0.46.
4. The fiber laser with the function of resisting the fiber core Raman echo according to claim 1, wherein in the single-mode fiber, the fiber core diameter is 4-6 μm, the fiber core numerical aperture is 0.08-0.12, the cladding diameter is 125 μm, and the output fiber of the indicating laser (1) and the first Raman isolation unit (2) are welded in a mode of aligning the fiber core axis.
5. The fiber laser with the function of resisting core Raman echo according to claim 4, wherein the center wavelength of the indicating laser output by the indicating laser (1) is 635nm, and the indicating laser is output along the core of the output fiber of the indicating laser (1) after sequentially passing through the first Raman isolation unit (2), the fiber oscillator resonant cavity (3), the second Raman isolation unit (4) and the QBH output fiber (5).
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