CN113555760A - System and method for dynamically regulating and controlling optical fiber laser mode - Google Patents
System and method for dynamically regulating and controlling optical fiber laser mode Download PDFInfo
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- CN113555760A CN113555760A CN202111104784.9A CN202111104784A CN113555760A CN 113555760 A CN113555760 A CN 113555760A CN 202111104784 A CN202111104784 A CN 202111104784A CN 113555760 A CN113555760 A CN 113555760A
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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
- H01S3/06754—Fibre amplifiers
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
- B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
- B23K26/062—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam
- B23K26/0622—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam by shaping pulses
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/70—Auxiliary operations or equipment
- B23K26/702—Auxiliary equipment
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Abstract
The invention relates to the technical field of fiber lasers, in particular to a system and a method for dynamically regulating and controlling a fiber laser mode, wherein the system comprises a seed source module, a power amplification module and an output module; the seed source module is composed of a fiber laser oscillator with adjustable wavelength and power; the power amplification module consists of a few-mode gain fiber and a pumping source and realizes the power amplification of seed light; the amplified laser is output through an output module and is used for industrial processing; the small mode gain fiber can internally generate a thermally induced transverse mode instability effect TMI. The invention has the advantages of low cost, strong stability and simple and convenient operation, and can realize mode regulation in a high-power range.
Description
Technical Field
The invention relates to the technical field of fiber lasers, in particular to a system and a method for dynamically regulating and controlling a fiber laser mode.
Background
The fiber laser has the advantages of good beam quality, high conversion efficiency, convenient heat management, compact structure and the like, has incomparable advantages in industrial application, and particularly has more obvious advantages in the processing of metal materials. However, since the fiber laser has high energy density, a large amount of metal vapor is generated after the solid metal absorbs the laser energy, and the gaseous metal carries away the liquid metal to generate a large amount of metal spatters. Part of particles generated by splashing is attached to the surface of the workpiece, so that the surface roughness of the workpiece is changed, and the processing quality is influenced; meanwhile, the other part of the optical fiber is attached to an optical element of the processing probe, so that the surface of the optical element is polluted, and the optical element and the optical fiber laser system are damaged in severe cases. Spatter control has become an indispensable part of the laser machining process.
The existing splash control technology generally changes the energy distribution of output laser spots through a mode conversion control system, avoids the over-high local temperature of metal materials, and effectively reduces the generation of gaseous metal, thereby inhibiting the splash. The existing mode conversion is mainly divided into two modes according to its working principle and mode. One is to modulate the spatial light field with a spatial light path and excite higher order modes in the fiber, thereby changing the laser mode. The other is to convert the laser mode by using a fiber mode coupler, such as a fiber grating, a multi-cladding ring fiber, and the like.
The spatial light path modulation method has high requirements on the coupling precision of the system, is difficult, and has high mode conversion efficiency easily interfered by environmental factors. The mode coupler has high difficulty and high cost in the manufacturing process, and the mode conversion efficiency is influenced by the manufacturing process.
Disclosure of Invention
It is an object of the present invention to provide a system and method for dynamic regulation of fiber laser modes that overcomes some or all of the disadvantages of the prior art.
The invention discloses a dynamic regulation and control system of an optical fiber laser mode, which comprises a seed source module, a power amplification module and an output module; the seed source module is composed of a fiber laser oscillator with adjustable wavelength and power; the power amplification module consists of a few-mode gain fiber and a pumping source and realizes the power amplification of seed light; the amplified laser is output through an output module and is used for industrial processing;
the small mode gain fiber can internally generate a thermally induced transverse mode instability effect TMI.
The invention provides a dynamic regulation and control method of an optical fiber laser mode, which adopts the dynamic regulation and control system of the optical fiber laser mode and comprises the following steps: the wavelength or the power of the seed light or the combination of the wavelength and the power of the seed light is controlled to control the threshold value of the TMI (thermally induced transverse mode instability) so as to dynamically regulate the appearance of the laser spot.
Preferably, the method for dynamically regulating and controlling the spot morphology of the laser through the power comprises the following steps: when the output power is lower than the TMI threshold, the output laser is in a laser fundamental mode LP01 mode, the shape of a light spot is stable, when the output power exceeds the threshold, the TMI effect occurs, and the energy of the light spot can be coupled back and forth between the laser fundamental mode LP01 and the high-order mode LP 11.
Preferably, the back-and-forth coupling mode is as follows: the intensity at the center of the corresponding spot fluctuates and the laser will switch modes, operating in LP01 mode when at the peak and LP11 mode when at the valley.
Preferably, the period of the mode transition is in the order of ms.
Preferably, when TMI effects occur, the spot morphology is equivalent to an incoherent superposition of the LP01 mode and the LP11 mode.
Preferably, when the TMI effect occurs, the corresponding light spot energy distribution is converted from the Gaussian distribution before regulation into the saddle-shaped distribution after regulation, and the light spot energy is even and smooth and is used for controlling the splashing effect in the laser processing.
The invention designs an optical fiber laser mode dynamic regulation and control system based on a thermally-induced mode unstable effect based on the principle that the thermally-induced transverse mode unstable effect in few-mode optical fibers causes dynamic conversion of a laser mode. Compared with the existing mode conversion system, the method provided by the invention does not need to add additional devices or control systems, has low cost, strong stability and simple and convenient operation, and can realize mode regulation and control in a high-power range.
Drawings
Fig. 1 is a schematic diagram of a system for dynamically adjusting and controlling a fiber laser mode in embodiment 1;
FIG. 2(a) is a schematic diagram illustrating the mode coupling process when the transverse mode instability effect occurs in example 1;
FIG. 2(b) is a graph showing the change of the central light intensity of the light spot with time when the lateral mode instability effect occurs in example 1;
FIG. 2(c) is a schematic diagram of the equivalent spot profile when the transverse mode instability effect occurs in example 1;
FIG. 2(d) is a schematic view showing light intensity distribution before and after adjustment when the transverse mode instability effect occurs in example 1;
FIG. 3(a) is a graph showing the variation of the threshold of the transverse mode instability effect with the optical power of the seed in example 1;
FIG. 3(b) is a graph showing the variation of the threshold of the lateral mode instability effect with the wavelength of the seed light in example 1.
Detailed Description
For a further understanding of the invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings and examples. It is to be understood that the examples are illustrative of the invention and not limiting.
Example 1
The existing all-fiber mode conversion system mainly utilizes a mode converter and realizes mode conversion between a fundamental mode and a high-order mode based on a mode coupling theory. The mode conversion result mainly depends on the structural characteristics of the mode conversion device, and simple and effective dynamic regulation and control cannot be realized. The embodiment designs an optical fiber laser mode dynamic regulation and control system based on a thermally-induced mode unstable effect based on the principle that the thermally-induced mode unstable effect in a few-mode optical fiber causes dynamic conversion of a transverse mode. The system schematic diagram is shown in fig. 1, and the whole system includes a seed source module, a power amplification module and an output module. Wherein the seed source module is composed of a fiber laser oscillator with adjustable wavelength and power; the power amplification module consists of a few-mode gain fiber and a pumping source and realizes the power amplification of seed light; the amplified laser is output through an output module and used for industrial processing.
In the gain fiber, a laser fundamental mode (LP01) and a high-order mode (LP11) generate interference fringes in the longitudinal direction of a fiber core, the interference fringes can generate periodic refractive index changes in the fiber core, namely a thermal long-period refractive index grating, the thermal refractive index grating can cause energy coupling of an LP01 mode and an LP11 mode, so that new interference fringes are generated, the new interference fringes can generate a new thermal refractive index grating, and the repeated process is repeated, so that the light spot energy can be coupled back and forth between the LP01 mode and the high LP11 mode, namely a thermal transverse mode instability effect (TMI) occurs inside the gain fiber. When the output power is lower than the TMI threshold, the output laser is in a pure LP01 mode, the spot morphology is stable, and when the output power exceeds the threshold, the spot energy will couple back and forth between LP01 and LP11 due to the TMI effect, as shown in fig. 2 (a). The intensity at the center of the corresponding spot fluctuates as shown in fig. 2(b), and when at the peak, the laser operates in LP01 mode, and when at the valley, the laser operates in LP11 mode. The period of such mode conversion is typically in the order of ms, and accordingly, when thermally induced transverse mode instability effects occur, the spot morphology can be equivalent to the incoherent superposition of the LP01 mode and the LP11 mode, as shown in fig. 2 (c); the corresponding light spot energy distribution is converted from gaussian distribution before regulation into saddle-shaped distribution after regulation, as shown in fig. 2(d), the light spot energy is even and smooth, and thus the splashing effect in laser processing is controlled.
In consideration of the fact that the output power of a laser needs to be adjustable in real time according to the processing requirements in actual industrial processing, the realization of the regulation and control of the high-power range of the laser mode can meet the requirements of laser processing on the laser power and the spot morphology. The invention can control the threshold value of the thermolabile transverse mode instability effect by adjusting and controlling the wavelength and the power of the seed light, thereby realizing the function. As shown in fig. 3(a), the optical power of the seed is increased from 10W to 300W, and the threshold of the transverse mode instability effect can be adjusted in a wide range; also as shown in fig. 3(b), the threshold of the lateral mode instability effect can also be adjusted in a wide range as the seed light wavelength is increased from 1018 nm to 1080 nm. In addition to the single regulation of the wavelength and the power of the seed light, the mode regulation in a larger power range can be realized by simultaneously controlling the wavelength and the power of the seed light.
Compared with the existing all-fiber mode conversion system, the novel mode conversion system has the advantages that:
1. the system does not depend on a mode converter, has a simpler structure and is lower in system building cost;
2. mode regulation can be realized at any power level according to processing requirements, and the regulation and control method is concise and sensitive and has wide application range.
The dynamic regulation and control mode based on the thermally induced transverse mode instability effect is not limited to regulating and controlling the power and wavelength of the seed light, and any mode for realizing the threshold regulation and control of the transverse mode instability effect can be adopted, such as dynamically regulating and controlling the power ratio, the wavelength of the pump light, the high-order mode ratio of the seed light, the line width of the seed light, the bending mode and the bending radius of the optical fiber, the core cladding ratio of the gain optical fiber, the doping mode of the gain optical fiber and the like in the bidirectional pumping structure.
The mode dynamic regulation and control system is not limited to a laser amplifier structure and can be used for any laser system.
The present invention and its embodiments have been described above schematically, without limitation, and what is shown in the drawings is only one of the embodiments of the present invention, and the actual structure is not limited thereto. Therefore, if the person skilled in the art receives the teaching, without departing from the spirit of the invention, the person skilled in the art shall not inventively design the similar structural modes and embodiments to the technical solution, but shall fall within the scope of the invention.
Claims (6)
1. The utility model provides a fiber laser mode dynamic control system which characterized in that: the device comprises a seed source module, a power amplification module and an output module; the seed source module is composed of a fiber laser oscillator with adjustable wavelength and power; the power amplification module consists of a few-mode gain fiber and a pumping source and realizes the power amplification of seed light; the amplified laser is output through an output module and is used for industrial processing;
the small mode gain fiber can internally generate a thermally induced transverse mode instability effect TMI.
2. A dynamic regulation and control method of an optical fiber laser mode is characterized in that: the optical fiber laser mode dynamic regulation and control system as claimed in claim 1 is adopted, and comprises: the wavelength or the power of the seed light or the combination of the wavelength and the power of the seed light is controlled to control the threshold value of the TMI (thermally induced transverse mode instability) so as to dynamically regulate the appearance of the laser spot.
3. The method for dynamically regulating the fiber laser mode according to claim 2, wherein the method comprises the following steps: the method for dynamically regulating and controlling the spot morphology of the laser through power comprises the following steps: when the output power is lower than the TMI threshold, the output laser is in a laser fundamental mode LP01 mode, the shape of a light spot is stable, when the output power exceeds the threshold, the TMI effect occurs, and the energy of the light spot can be coupled back and forth between the laser fundamental mode LP01 and the high-order mode LP 11.
4. The method for dynamically regulating the fiber laser mode according to claim 3, wherein the method comprises the following steps: the back-and-forth coupling mode is as follows: the intensity at the center of the corresponding spot fluctuates and the laser will switch modes, operating in LP01 mode when at the peak and LP11 mode when at the valley.
5. The method of claim 4, wherein the method comprises: the periodicity of the mode transition is in the order of ms.
6. The method of claim 5, wherein the method comprises: when TMI effect occurs, the light spot morphology is equivalent to incoherent superposition of an LP01 mode and an LP11 mode; the corresponding light spot energy distribution is converted from Gaussian distribution before regulation and control into saddle-shaped distribution after regulation and control, and the light spot energy is even and smooth.
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| CN202111104784.9A CN113555760A (en) | 2021-09-22 | 2021-09-22 | System and method for dynamically regulating and controlling optical fiber laser mode |
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| CN202111104784.9A CN113555760A (en) | 2021-09-22 | 2021-09-22 | System and method for dynamically regulating and controlling optical fiber laser mode |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116539279A (en) * | 2023-03-13 | 2023-08-04 | 中国工程物理研究院激光聚变研究中心 | Measuring system and measuring method for absorption coefficient of cladding pumping light |
| CN118033901A (en) * | 2024-04-11 | 2024-05-14 | 中国工程物理研究院激光聚变研究中心 | Coiling method and system for fiber core diameter and refractive index longitudinal variation gain fiber |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116539279A (en) * | 2023-03-13 | 2023-08-04 | 中国工程物理研究院激光聚变研究中心 | Measuring system and measuring method for absorption coefficient of cladding pumping light |
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| CN118033901A (en) * | 2024-04-11 | 2024-05-14 | 中国工程物理研究院激光聚变研究中心 | Coiling method and system for fiber core diameter and refractive index longitudinal variation gain fiber |
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