Narrow linewidth fiber laser system with high SBS threshold value and high TMI threshold value

Abstract

The invention provides a narrow linewidth fiber laser system with a high SBS threshold value and a high TMI threshold value, the narrow linewidth fiber laser system comprises a narrow linewidth continuous signal source, a signal modulator, a pumping source output device, a beam combiner and a gain fiber, after the linewidth continuous signal source outputs continuous narrow linewidth laser, the narrow linewidth laser passes through the signal modulator, and the pumping source output device outputs the narrow linewidth laser through the beam combiner. The duration time of the narrow linewidth laser is modulated to nanosecond magnitude by a signal modulator to form signal light, and meanwhile, the pumping source output device continuously outputs pumping light of which the pumping light period is matched with the thermally induced refractive index grating period of the gain optical fiber; signal light output by the narrow linewidth continuous signal source and pump light output by the pump source output device are efficiently coupled into the same optical fiber through the beam combiner to form beam-combined laser, and then the beam-combined laser is output by the gain optical fiber. In the process, the signals and the pumping source are modulated at the same time, so that the all-fiber laser has the advantages of being all-fiber, high in SBS threshold value, high in TMI threshold value and the like.

Description

Technical Field

[0001] The invention relates to the technical field of narrow-linewidth fiber laser systems, and in particular to a narrow-linewidth fiber laser system with a high SBS threshold and a high TMI threshold. Background Art

[0002] High-power narrow-linewidth fiber lasers have important application value in industrial processing, scientific research, national defense security, etc. However, with the increase of output power, nonlinear effects and mode instability effects begin to appear, becoming the key factors that hinder narrow-linewidth fiber lasers from achieving higher power output.

[0003] Among many nonlinear effects, stimulated Brillouin scattering (SBS) is the first nonlinear effect to appear. It is an effect produced by the interaction between signal light, Stokes light and acoustic waves, and has obvious threshold characteristics. When the threshold is exceeded, the signal light power will be transferred to the backward Stokes light in large quantities, which will have serious harm to the safety of the device and the stability of the laser system. Transverse mode instability (TMI) is a new phenomenon discovered in 2010. It originates from thermal gratings in optical fibers and also has obvious threshold effects. When the threshold of the mode instability effect is exceeded, the power will undergo irregular conversion between the fundamental mode and the higher-order mode, reducing the output power and beam quality.

[0004] Researchers have continued to explore the above two factors, but there are incompatibility between the suppression measures for the two effects. For example, increasing the mode field area can reduce the core power density and increase the stimulated Brillouin scattering threshold, but the increase in the mode field area leads to a large increase in the number of modes that the fiber can support, which will reduce the threshold of the mode instability effect; reducing the absorption coefficient of the gain fiber will increase the threshold of the mode instability effect, but in order to ensure the absorption efficiency of the pump light, reducing the absorption coefficient of the gain fiber will increase the fiber length, which will reduce the stimulated Brillouin scattering threshold. Summary of the invention

[0005] The present invention provides a narrow-linewidth fiber laser system with high SBS threshold and high TMI threshold, which is used to solve the technical problem that the suppression measures for SBS threshold and TMI threshold in the prior art are incompatible.

[0006] The embodiment of the present application provides a narrow linewidth fiber laser system with a high SBS threshold and a high TMI threshold, comprising:

[0007] Narrow line width continuous signal source, used to output continuous narrow line width laser;

[0008] A signal modulator, which is arranged at the output end of the narrow linewidth continuous signal source and is used to modulate the duration of the narrow linewidth laser to the nanosecond level to output modulated signal light;

[0009] A pump source output device, used for outputting pump light;

[0010] A beam combiner, wherein a first input end of the beam combiner is connected to an output end of the signal modulator, a second input end of the beam combiner is connected to the pump source output device, and the beam combiner is used to combine the signal light and the pump light to obtain a combined laser;

[0011] A gain optical fiber, the end of which is connected to the output end of the beam combiner, and is used to output the combined laser beam;

[0012] Wherein, the pump light period output by the pump source output device matches the thermal refractive index grating period of the gain optical fiber.

[0013] In some embodiments, the signal modulator includes a radio frequency controller and an intensity modulator, the input end of the intensity modulator is connected to the output end of the narrow linewidth continuous signal source, the output end of the intensity modulator is connected to the first end of the combiner, and the radio frequency controller is connected to the control end of the intensity modulator.

[0014] In some embodiments, the pump source output device includes a pump source continuous output device and a current controller, wherein the output end of the pump source continuous output device is connected to the second input end of the combiner for outputting continuous pump light; the current controller is connected to the control end of the pump source continuous output device for adjusting the output period of the pump source continuous output device outputting the pump light.

[0015] In some embodiments, an isolator is further included, which is arranged between the signal modulator and the combiner, the input end of the isolator is connected to the output end of the signal modulator, and the output end of the isolator is connected to the first output of the combiner.

[0016] In some embodiments, a cladding light stripper is further included, and the cladding light stripper is disposed at an end of the gain fiber away from the combiner.

[0017] In some embodiments, the narrow linewidth continuous signal source is one of a fiber laser, a semiconductor laser, and a solid laser.

[0018] In some embodiments, the narrow linewidth continuous signal source has a wavelength of 1-2 microns.

[0019] In some embodiments, the narrow linewidth continuous signal source, the pump source output device, the signal modulator, the beam combiner and the gain fiber are all fusion-spliced ​​by a fiber fusion splicer.

[0020] In some embodiments, an output end cap is further included, wherein the output end cap is disposed at the output end of the cladding light stripper.

[0021] In some embodiments, the output end cap is made of quartz material.

[0022] Beneficial effects: The present application provides a narrow linewidth fiber laser system with high SBS threshold and high TMI threshold, which relates to the technical field of narrow linewidth fiber laser system, including a narrow linewidth continuous signal source, a signal modulator, a pump source output device, a beam combiner and a gain fiber. After the linewidth continuous signal source outputs continuous narrow linewidth laser, the narrow linewidth laser passes through the signal modulator, and the signal modulator modulates the duration of the narrow linewidth laser to the nanosecond level to form a signal light that can reduce the action time of the Stoekes light to the nanosecond level. At the same time, the pump source output device continuously outputs pump light whose pump light period matches the period of the thermal refractive index grating of the gain fiber. The signal light output by the narrow linewidth continuous signal source and the pump light output by the pump source output device are efficiently coupled into the same optical fiber through the beam combiner to form a combined laser, which is then output by the gain fiber. In this process, by simultaneously modulating the signal and the pump source, the present invention has the advantages of all-fiber, high SBS threshold and high TMI threshold. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A framework diagram of a narrow-linewidth fiber laser system with a high SBS threshold and a high TMI threshold is provided for an embodiment of the present application.

[0024] Description of Reference Numerals

[0025] 1. Narrow linewidth continuous signal source; 2. RF controller; 3. Intensity modulator;

[0026] 4. Isolator; 5. Pump source continuous output device; 6. Current controller;

[0027] 7. Beam combiner; 8. Gain fiber; 9. Output end cap; 10. Cladding light stripper. DETAILED DESCRIPTION

[0028] The following embodiments of the technical solution of the present application will be described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0030] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0031] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0032] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0033] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0034] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the embodiments of the present application.

[0035] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0036] High-power narrow-linewidth fiber lasers have important application value in industrial processing, scientific research, national defense security, etc. However, with the increase of output power, nonlinear effects and mode instability effects begin to appear, becoming the key factors that hinder narrow-linewidth fiber lasers from achieving higher power output.

[0037] Among many nonlinear effects, stimulated Brillouin scattering (SBS) is the first nonlinear effect to appear. It is an effect produced by the interaction between signal light, Stokes light and acoustic waves, and has obvious threshold characteristics. When the threshold is exceeded, the signal light power will be transferred to the backward Stokes light in large quantities, which will have serious harm to the safety of the device and the stability of the laser system. Transverse mode instability (TMI) is a new phenomenon discovered in 2010. It originates from thermal gratings in optical fibers and also has obvious threshold effects. When the threshold of the mode instability effect is exceeded, the power will undergo irregular conversion between the fundamental mode and the higher-order mode, reducing the output power and beam quality.

[0038] Researchers have continued to explore the above two factors, but there are incompatibility between the suppression measures for the two effects. For example, increasing the mode field area can reduce the core power density and increase the stimulated Brillouin scattering threshold, but the increase in the mode field area leads to a large increase in the number of modes that the fiber can support, which will reduce the threshold of the mode instability effect; reducing the absorption coefficient of the gain fiber 8 will increase the threshold of the mode instability effect, but in order to ensure the absorption efficiency of the pump light, reducing the absorption coefficient of the gain fiber 8 will increase the fiber length, which reduces the stimulated Brillouin scattering threshold.

[0039] In order to solve the technical problem of incompatibility of the suppression measures for the SBS threshold and the TMI threshold in the prior art, the present invention provides a narrow-linewidth fiber laser system with a high SBS threshold and a high TMI threshold. By simultaneously modulating the signal and the pump source, the present invention has the advantages of all-fiber, high SBS threshold and high TMI threshold.

[0040] Please refer to Figure 1 , Figure 1A framework diagram of a narrow-linewidth fiber laser system with a high SBS threshold and a high TMI threshold is provided for an embodiment of the present application, comprising: a narrow-linewidth continuous signal source 1, a signal modulator, a pump source output device, a combiner 7 and a gain fiber 8, wherein the narrow-linewidth continuous signal source 1 is used to output a continuous narrow-linewidth laser; the signal modulator is arranged at the output end of the narrow-linewidth continuous signal source 1, and is used to modulate the duration of the narrow-linewidth laser to the nanosecond level, and output the modulated signal light; and the pump source output device is used to output the pump light; the first input end of the combiner 7 is connected to the output end of the signal modulator, and the second input end of the combiner 7 is connected to the pump source output device, and the combiner 7 is used to combine the signal light and the pump light to obtain a combined laser; the gain fiber 8, the end of the gain fiber 8 is connected to the output end of the combiner 7, and is used to output the combined laser; wherein the pump light period output by the pump source output device matches the thermal refractive index grating period of the gain fiber 8.

[0041] Specifically, in this embodiment, after the narrow linewidth continuous signal source 1 outputs continuous narrow linewidth laser light, the narrow linewidth laser light passes through the signal modulator, and the signal modulator modulates the duration of the narrow linewidth laser light to the nanosecond level, so as to form a signal light whose action time with the Stokes light is reduced to the nanosecond level. At the same time, the pump source output device continuously outputs the pump light whose pump light period matches the period of the thermo-induced refractive index grating of the gain fiber 8. The signal light output by the narrow linewidth continuous signal source 1 and the pump light output by the pump source output device are efficiently coupled into the same optical fiber through the beam combiner 7, and a combined laser light is formed, which is then output by the gain fiber 8. In this process, since the signal light output by the linewidth continuous signal source and the pump light output by the pump source output device are both continuously output, the thermo-induced refractive index grating in the gain fiber 8 can exist stably; and when the threshold is reached, the power will be converted between the fundamental mode and the high-order mode. At the same time, the signal light and the Stokes light will interact with each other throughout the entire length of the optical fiber, that is, the Stokes light will be continuously amplified in the optical fiber. When the period of the pump light output by the pump source output device can match the period of the thermo-refractive index grating, the thermo-refractive index grating in the gain fiber 8 will be disturbed or weakened, so that the energy conversion between the fundamental mode and the high-order mode is weakened, and the TMI threshold of the system can be improved. At the same time, the output power of the narrow linewidth fiber laser system will show a periodic output synchronized with the pump in the time domain. However, according to the characteristics of the thermo-refractive index grating in the gain fiber 8, the modulation period of the pump source output device is in the millisecond level, which is 6 orders of magnitude different from the occurrence scale of the stimulated Brillouin scattering process (nanosecond level). Therefore, for stimulated Brillouin scattering, the threshold will be determined by the highest power of the signal light rather than the average power. Therefore, although the single use of pump source modulation can improve the TMI threshold, it has no effect on the improvement of the stimulated Brillouin scattering threshold. Stimulated Brillouin scattering is a nonlinear effect occurring between the signal light and the Stokes light, and its time scale is in the nanosecond level. Therefore, if the stimulated Brillouin scattering threshold is to be increased, the action time of the signal light and the Stoekes light needs to be reduced to the nanosecond level, that is, the time scale of the signal light should be in the nanosecond level, and at this time the stimulated Brillouin scattering process will not be effectively stimulated, thereby increasing the SBS threshold. Therefore, in this embodiment, through signal modulation (and pump source modulation, the entire system has the effects of high SBS threshold and high TMI threshold at the same time.

[0042] Furthermore, in the embodiment provided in the present application, the signal modulator includes a radio frequency controller 2 and an intensity modulator 3, the input end of the intensity modulator 3 is connected to the output end of the narrow linewidth continuous signal source 1, the output end of the intensity modulator 3 is connected to the first end of the combiner 7, and the radio frequency controller 2 is connected to the control end of the intensity modulator 3. In the present embodiment, the radio frequency controller 2 provides an adjustable radio frequency drive signal to determine the pulse parameters; after receiving the adjustable radio frequency drive signal provided by the radio frequency controller 2, the intensity modulator 3 adjusts the light intensity according to the radio frequency drive signal to realize the pulse of the optical signal, and then modulates the duration of the narrow linewidth laser to the nanosecond level to form a signal light that can reduce the action time with the Stoekes light to the nanosecond level.

[0043] Furthermore, in the embodiment provided in the present application, the pump source output device includes a pump source continuous output device 5 and a current controller 6. The output end of the pump source continuous output device 5 is connected to the second input end of the combiner 7 for outputting continuous pump light. The current controller 6 is connected to the control end of the pump source continuous output device 5 for adjusting the output period of the pump light output by the pump source continuous output device 5. In the present embodiment, the output period of the pump light output by the pump source continuous output device 5 is controlled by the current controller 6, so that the period of the pump light output by the pump source continuous output device 5 can match the period of the thermorefractive index grating, thereby disrupting or weakening the thermorefractive index grating in the gain fiber 8, so that the energy conversion between the fundamental mode and the high-order mode is weakened, thereby improving the TMI threshold of the system.

[0044] Furthermore, in the embodiment provided in the present application, an isolator 4 is also included, which is arranged between the signal modulator and the combiner 7. The input end of the isolator 4 is connected to the output end of the signal modulator, and the output end of the isolator 4 is connected to the first output of the combiner 7. In this embodiment, the isolator 4 can effectively prevent the reverse propagating light from entering the narrow linewidth continuous signal source 1 or the signal modulator, thereby ensuring the stable operation of the laser; secondly, the isolator 4 also improves the system efficiency and protects other optical components.

[0045] In some embodiments, a cladding light stripper 10 is further included. The cladding light stripper 10 is arranged at one end of the gain fiber 8 away from the combiner 7. In this embodiment, the cladding light stripper can strip off the excess light propagating in the optical fiber cladding to prevent it from interfering with signal light transmission or damaging the optical fiber system, thereby ensuring the efficient operation of the system and the quality of the output light beam.

[0046] Furthermore, in the embodiment provided in the present application, the narrow linewidth continuous signal source 1 is one of a fiber laser, a semiconductor laser, and a solid laser.

[0047] Specifically, fiber lasers are doped with rare earth ions (such as erbium-doped 3+、Ytterbium-doped 3 +) optical fiber is used as the gain medium. The pump light is coupled into the optical fiber to excite the rare earth ions, thereby generating stimulated radiation. The fiber laser utilizes a long fiber resonant cavity and a fiber Bragg grating (FBG) to achieve an extremely narrow linewidth. Secondly, the fiber structure of the fiber laser can provide excellent thermal management and resistance to environmental interference, and is particularly suitable for long-term stable operation.

[0048] Semiconductor lasers use carrier recombination in PN junctions to generate stimulated radiation, and photons form a resonant cavity in the semiconductor gain region. Semiconductor lasers can achieve narrow linewidth output through external cavity design (such as external cavity semiconductor lasers, ECDL) or integrated optical feedback technology. Semiconductor lasers are compact and have a wide tunable range, making them suitable for applications that require flexible wavelength selection.

[0049] Solid-state lasers use solid gain media (such as Nd 3 + yttrium aluminum garnet Nd:YAG) as the working material, pump light (usually semiconductor laser) excites rare earth ions in the gain medium, thereby generating stimulated radiation. Solid-state lasers have high output spectrum stability and power stability due to the excellent optical properties of solid gain media.

[0050] In this embodiment, by selecting a suitable laser type according to specific needs, system performance can be optimized and application requirements can be met.

[0051] Furthermore, in the embodiment provided in the present application, the wavelength of the narrow linewidth continuous signal source 1 is 1-2 microns.

[0052] Furthermore, in the embodiment provided in the present application, the narrow linewidth continuous signal source 1, the pump source output device, the signal modulator, the beam combiner 7 and the gain fiber 8 are all fused by a fiber fusion splicer, which can effectively avoid the scattering or mode mismatch of the light beam at the connection interface, thereby ensuring the mode quality of the signal. Secondly, the cavity noise caused by reflection or scattering is avoided by fusion, thereby maintaining the high spectral purity of the narrow linewidth signal. For components such as pump sources and signal modulators, the fusion connection prevents excess reflected light from entering the system, ensuring the stability of the system operation, which can not only significantly improve the optical performance, mechanical reliability and stability of the system, but also reduce assembly complexity and improve integration.

[0053] Furthermore, in the embodiment provided in the present application, an output end cap 9 is also included. The output end cap 9 is arranged at the output end of the cladding light stripper. The output end cap 9 can not only effectively isolate the external environment and prevent dust, moisture and other impurities from contaminating the optical fiber end face, thereby ensuring the optical performance and system stability, but the output end cap 9 can also adopt a special anti-reflection coating or be designed into an angled structure to reduce the interference of laser return light on the system, optimize the light beam divergence angle and intensity distribution, make the output laser more stable, thereby improving the light beam quality.

[0054] Furthermore, in the embodiment provided in the present application, the output end cap 9 is made of quartz material. The output end cap 9 made of quartz material has extremely high optical transmittance, which can ensure efficient output of the laser signal and thus reduce light loss.

[0055] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A narrow linewidth fiber laser system with high SBS threshold and high TMI threshold, characterized in that: include: Narrow line width continuous signal source, used to output continuous narrow line width laser; A signal modulator, which is arranged at the output end of the narrow linewidth continuous signal source and is used to modulate the duration of the narrow linewidth laser to the nanosecond level to output modulated signal light; A pump source output device, used for outputting pump light; A beam combiner, wherein a first input end of the beam combiner is connected to an output end of the signal modulator, a second input end of the beam combiner is connected to the pump source output device, and the beam combiner is used to combine the signal light and the pump light to obtain a combined laser; A gain optical fiber, the end of which is connected to the output end of the beam combiner, and is used to output the combined laser beam; Wherein, the pump light period output by the pump source output device matches the thermal refractive index grating period of the gain optical fiber.

2. The narrow linewidth fiber laser system with high SBS threshold and high TMI threshold according to claim 1, characterized in that: The signal modulator includes a radio frequency controller and an intensity modulator, the input end of the intensity modulator is connected to the output end of the narrow linewidth continuous signal source, the output end of the intensity modulator is connected to the first end of the combiner, and the radio frequency controller is connected to the control end of the intensity modulator.

3. The narrow linewidth fiber laser system with high SBS threshold and high TMI threshold according to claim 1, characterized in that: The pump source output device includes a pump source continuous output device and a current controller. The output end of the pump source continuous output device is connected to the second input end of the beam combiner for outputting continuous pump light. The current controller is connected to the control end of the pump source continuous output device for adjusting the output period of the pump source continuous output device outputting the pump light.

4. The narrow linewidth fiber laser system with high SBS threshold and high TMI threshold according to claim 1, characterized in that: It also includes an isolator, which is arranged between the signal modulator and the beam combiner, wherein the input end of the isolator is connected to the output end of the signal modulator, and the output end of the isolator is connected to the first output of the beam combiner.

5. The narrow linewidth fiber laser system with high SBS threshold and high TMI threshold according to claim 1, characterized in that: It also includes a cladding light stripper, which is arranged at one end of the gain optical fiber away from the beam combiner.

6. The narrow linewidth fiber laser system with high SBS threshold and high TMI threshold according to claim 1, characterized in that: The narrow linewidth continuous signal source is one of a fiber laser, a semiconductor laser, and a solid laser.

7. The narrow linewidth fiber laser system with high SBS threshold and high TMI threshold according to claim 1, characterized in that: The wavelength of the narrow linewidth continuous signal source is 1-2 microns.

8. The narrow linewidth fiber laser system with high SBS threshold and high TMI threshold according to claim 1, characterized in that: The narrow linewidth continuous signal source, the pump source output device, the signal modulator, the beam combiner and the gain optical fiber are all fusion-spliced ​​by an optical fiber fusion splicer.

9. The narrow linewidth fiber laser system with high SBS threshold and high TMI threshold according to claim 5, characterized in that: The device also includes an output end cap, which is disposed at the output end of the cladding light stripper.

10. The narrow linewidth fiber laser system with high SBS threshold and high TMI threshold according to claim 9, characterized in that: The output end cap is made of quartz material.

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