High repetition frequency polarization-maintaining ytterbium-doped fiber laser

Abstract

The invention relates to the technical field of lasers, in particular to a high-repetition-frequency polarization-maintaining ytterbium-doped fiber laser which comprises a seed pump source module and a seed source module. The seed pump source module comprises a first pump source used for outputting pump light of a first wavelength; the first resonant cavity comprises a first gain medium and a first reflection unit used for reflecting the pump light with the first wavelength, and is used for absorbing the pump light with the first wavelength and outputting pump light with a second wavelength; the seed source module comprises a second resonant cavity which comprises a second gain medium and a second reflection unit used for reflecting the pump light of the second wavelength and is used for absorbing the pump light of the second wavelength and outputting signal light of a third wavelength. The spontaneous radiation gain is reduced by reducing the excited state population inversion degree, the damage risk of the fiber laser is reduced, and the pulse and power stability can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lasers, and particularly to a high-repetition-rate polarization-maintaining ytterbium-doped fiber laser. Background Art

[0002] Infrared light, as an important form of electromagnetic radiation, exhibits indispensable value in numerous fields due to its unique physical properties. Its wavelength range is relatively broad, and different wavelength intervals possess diverse performance characteristics, thus adapting to a rich variety of application scenarios.

[0003] 1100nm infrared light occupies a special position in the entire infrared spectrum. In the field of biomedicine, due to its ability to penetrate deep into biological tissues, it can effectively reduce scattering and absorption within the tissue, thereby significantly improving imaging resolution, providing strong support for the clear observation of microscopic structures within the organism, and contributing to the early and accurate diagnosis and research of diseases. In materials processing and manufacturing, its high energy density and precise controllability make it an ideal processing light source.

[0004] Currently, mainstream 1100nm fiber lasers mostly adopt the working mode of directly pumping a gain fiber with a 976nm LD pump source within a 1100nm high-low reflection grating resonator. However, this technical solution is prone to the spontaneous emission effect, which has the following impacts: 1. It leads to a decrease in energy conversion efficiency, such that the laser cannot efficiently convert the energy input by the pump source, resulting in energy waste; 2. It causes instability in pulses and power, affecting the quality and stability of the laser output by the laser, making the laser unable to adapt to application scenarios such as precision processing and high-end scientific research that require extremely high laser stability; 3. When the spontaneous emission effect reaches a certain level, it may directly damage the device, causing the laser to malfunction, increasing equipment maintenance costs and the risk of production interruption, and restricting the wide application and performance improvement of fiber lasers in more fields.

[0005] Therefore, how to address the deficiencies existing in the above-mentioned prior art has become the research topic to be solved by the present invention. Summary of the Invention

[0006] The object of the present invention is to provide a high-repetition-rate polarization-maintaining ytterbium-doped fiber laser.

[0007] To achieve the above object, the technical solution adopted by the present invention is: A high-repetition-rate polarization-maintaining ytterbium-doped fiber laser, comprising a seed pump source module having a first gain medium and a seed source module having a second gain medium; Both the first gain medium and the second gain medium are fibers doped with ytterbium ions; The seed pump source module includes a first pump source that can output pump light with a first wavelength; The seed pump source module is used to output pump light with a second wavelength to the seed source module; The seed source module is used to absorb the pump light with the second wavelength and output signal light with a third wavelength; The first wavelength is less than or equal to 976 nm; The second wavelength is greater than 976 nm and less than 1100 nm; The third wavelength is greater than or equal to 1100 nm.

[0008] In the above solution, in the present application, the pump light with the first wavelength is not directly input into the seed source module. Instead, the pump light with the first wavelength is converted into pump light with the second wavelength, and then the pump light with the second wavelength is input into the seed source module. By reducing the population inversion degree of excited states, the gain of spontaneous emission is reduced, the risk of damage to the fiber laser caused by the spontaneous emission effect is reduced, and it helps to improve the stability of pulses and power.

[0009] The present application reduces the risk of damage to the fiber laser, thereby reducing the equipment maintenance cost and the risk of production interruption, and further facilitating the wide application and performance improvement of the fiber laser in more fields.

[0010] The present application improves the stability of pulses and power, enabling the laser to stably output high-quality laser, and facilitating the laser to adapt to application scenarios such as precision machining and high-end scientific research that require extremely high laser stability.

[0011] The present application improves the energy conversion efficiency of the laser by reducing the gain of spontaneous emission, enabling the energy input by the pump source to be efficiently converted into the required signal light energy and improving the energy utilization rate.

[0012] In a further technical solution, the first wavelength is 976 nm; And / or, the second wavelength is 1030 nm; And / or, the third wavelength is 1100 nm.

[0013] It should be noted that taking the first gain medium as Yb gain fiber for illustration, currently, the mainstream pump light bands of Yb gain fiber are 915 nm and 976 nm, and 976 nm is a band with a relatively high absorption intensity of Yb ions; setting the first wavelength to 976 nm enables Yb ions to more effectively absorb the pump light energy, realize the transition from the ground state to the excited state, thereby improving the pump efficiency and enabling the Yb gain fiber to reach a higher gain level at a lower pump power.

[0014] It should also be noted that currently, the lasers emitted by Yb-doped gain fibers are 1030 nm and 1064 nm. Among them, 1030 nm is a wavelength band with a relatively high emission intensity of the Yb-doped gain fiber. By setting the second wavelength to 1030 nm, the Yb-doped gain fiber can more effectively convert the pump light energy into laser energy, achieving a relatively high laser output power and optical-optical conversion efficiency, and having a relatively high degree of suppression of the spontaneous emission phenomenon.

[0015] In a further technical solution, the seed pump source module includes a first resonant cavity, and the first gain medium forms part of the first resonant cavity; The output end of the first pump source is connected to the input end of the first resonant cavity; The first resonant cavity is configured to absorb the pump light of the first wavelength and output the pump light of the second wavelength; The first resonant cavity includes a first reflection unit for reflecting the pump light of the first wavelength.

[0016] The first reflection unit includes a first high-reflection grating (which can also be said to be a high-reflective grating, such as a 1030 nm high-reflection grating with a line width of 5 nm and a reflectivity range of 99% - 99.9%) and a first low-reflection grating (which can also be said to be a low-reflective grating, such as a 1030 nm low-reflection grating with a line width of 5 nm and a reflectivity range of 20% - 30%).

[0017] The working principle of a specific embodiment of the first resonant cavity is as follows: The first pump source outputs the pump light of the first wavelength into the first resonant cavity. Without considering repeated reflections, the pump light of the first wavelength sequentially passes through the first high-reflection grating, the first gain medium (the actual light-absorbing structure), and the first low-reflection grating, and finally forms the pump light of the second wavelength; the first high-reflection grating feeds back the light within a specific wavelength range into the first gain medium to prepare for the subsequent light amplification process; when the light propagates in the first gain medium, it interacts with the particles in the population inversion state, forms oscillations in the first resonant cavity, and the light intensity gradually increases; the light emitted from the first gain medium reaches the first low-reflection grating, a part of the light is reflected back into the first gain medium and continues to propagate and be further amplified in the first gain medium, which helps to maintain the oscillation of the light in the first resonant cavity, and the other part of the light passes through the first low-reflection grating and is output as the output light.

[0018] To help understanding, the above description of "interacting with particles in a state of particle population inversion" is supplemented here. For similar descriptions in this application, refer to this paragraph: Due to the injection of pump light, the low-energy level particles of rare earth ions in the first gain medium transition to high energy levels, achieving particle population inversion. When the number of high-energy level particles reaches a certain number, since the particles are at a high energy level, their state is unstable, so they will quickly return to the low energy level and radiate energy outward in the form of photons.

[0019] This embodiment clarifies the method of converting the pump light of the first wavelength into the pump light of the second wavelength, so as to achieve the stable output of the pump light of the second wavelength, thereby achieving the stable operation of the fiber laser.

[0020] In a further technical solution, the seed pump source module further includes a first beam combiner, and the output end of the first pump source is connected to the input end of the first resonant cavity through the first beam combiner; And / or, the seed pump source module further includes a first online isolator, and the output end of the first resonant cavity is connected to the input end of the first online isolator; And / or, the seed pump source module also includes a third gain medium, a second combiner and a second pump source, the third gain medium is an optical fiber doped with ytterbium ions, the first resonant cavity, the third gain medium, the second combiner and the second pump source are connected in sequence, and the third gain medium and the second pump source are used to cooperate to amplify the pump light of the second wavelength.

[0021] The first beam combiner can combine the pumping lights output by multiple pumping sources, thereby providing sufficient pumping lights for the fiber laser to meet the diverse requirements of the fiber laser for the power of the output light. The first pumping source can include multiple sub-pumping sources, and the same is true for the second pumping source described below.

[0022] The first in-line isolator is used to prevent the light from propagating in the reverse direction after leaving the first resonant cavity, thereby improving the stability and reliability of the fiber laser. In some embodiments, the first in-line isolator is disposed between the first resonant cavity and the third gain medium, and the output end of the first in-line isolator is connected to the input end of the third gain medium.

[0023] Before the seed pump source module outputs the pump light of the second wavelength to the seed source module, the third gain medium cooperates with the second pump source to amplify the pump light of the second wavelength, thereby providing sufficient pump light for the second resonant cavity in the seed source module to output the signal light of the third wavelength, thereby meeting the fiber laser's requirement for stable output of light of a specific wavelength.

[0024] In a further technical solution, the seed source module further includes a second resonant cavity, and the second gain medium constitutes a part of the second resonant cavity; The output end of the seed pump source module is connected to the input end of the second resonant cavity; The second resonant cavity is used to absorb the pump light of the second wavelength and output the signal light of the third wavelength; The second resonant cavity includes a second reflection unit for reflecting the pump light of the second wavelength.

[0025] The second reflection unit includes a second high-reflection grating (such as a 1100nm high-reflection grating, the line width can be 5nm, and the reflectivity ranges from 99% to 99.9%) and a second low-reflection grating (such as a 1100nm low-reflection grating, the line width can be 5nm, and the reflectivity ranges from 65% to 70%).

[0026] The working principle in a specific embodiment of the second resonant cavity is as follows: The seed pump source module outputs the pump light of the second wavelength into the second resonant cavity. Without considering repeated reflections, the pump light of the second wavelength sequentially passes through the second high-reflection grating, the second gain medium, and the second low-reflection grating, and finally forms the signal light of the third wavelength; the second high-reflection grating feeds back the light within a specific wavelength range into the second gain medium to prepare for the subsequent optical amplification process; when the light propagates in the second gain medium, it interacts with the particles in the population inversion state, forms oscillations in the second resonant cavity, and the light intensity gradually increases; the light emitted from the second gain medium reaches the second low-reflection grating, a part of the light is reflected back to the second gain medium and continues to propagate in the second gain medium and is further amplified, which helps to maintain the oscillation of the light in the second resonant cavity, and the other part of the light passes through the second low-reflection grating and is emitted as the output light.

[0027] The seed source module converts the pump light of the second wavelength into the signal light of the third wavelength through the second resonant cavity to meet the output requirements of the fiber laser for light of a specific wavelength.

[0028] In a further technical solution, the seed source module further includes a control switch disposed in the second resonant cavity.

[0029] The control switch can control the output of the signal light of the third wavelength.

[0030] In some embodiments, the control switch is disposed between the second gain medium and the second low-reflection grating, which can better achieve population inversion energy storage.

[0031] In a further technical solution, it further includes a fiber first-stage amplification module for amplifying the signal light of the third wavelength; The fiber first-stage amplification module includes a second in-line isolator, a mode matcher, a fourth gain medium, a third beam combiner, and a third pump source connected in sequence; The input end of the second in-line isolator is connected to the output end of the seed source module; The fourth gain medium is an optical fiber doped with ytterbium ions; the diameter of the optical fiber in the fourth gain medium is greater than the diameter of the optical fiber in the second gain medium; The fourth gain medium and the third pump source are used to cooperate to amplify the signal light of the third wavelength.

[0032] The actual optical amplification structure in the optical fiber primary amplification module is the fourth gain medium and the third pump source. The fourth gain medium and the third pump source can cooperate to achieve power amplification of the signal light of the third wavelength, thereby obtaining higher-power laser output, preparing for further increasing the laser power in the future to meet various application scenarios that require high-energy lasers and expand the scope of application of fiber lasers.

[0033] In the optical fiber primary amplifier module, the second online isolator is used to prevent light from propagating in the reverse direction after entering the optical fiber primary amplifier module, thereby avoiding damage to components (such as components in the seed source module) and improving the stability and reliability of the optical fiber laser. In some embodiments, the second online isolator is disposed between the second low-reflection grating and the mode matcher.

[0034] The purpose of the third beam combiner refers to the description of the first beam combiner.

[0035] The diameter of the optical fiber in the fourth gain medium is larger than that in the second gain medium. It can be considered that the optical fiber in the second gain medium is thinner, while the optical fiber in the fourth gain medium is thicker. Using an optical fiber with a thicker core diameter can increase the nonlinear threshold, thereby suppressing the generation of nonlinearity.

[0036] Since the diameter of the optical fiber in the fourth gain medium is different from the diameter of the optical fiber in the second gain medium, a mode matcher is set based on this to achieve efficient coupling and transmission of light between the two optical fibers.

[0037] It should be emphasized that the various structures in the optical fiber primary amplification module have a synergistic effect. The fourth gain medium and the third pump source cooperate to amplify the signal light of the third wavelength to achieve the purpose of optical power amplification, which will lead to the generation of nonlinear optical effects. Based on this, the thicker optical fiber in the fourth gain medium is used in conjunction with a mode matcher to solve this problem and ensure that the fiber laser can stably output high-power laser.

[0038] Nonlinear optical effects can cause some problems, such as causing the laser output power to no longer increase linearly with the pump power, limiting the development of fiber lasers toward high power. This is an existing impact and will not be explained in detail here.

[0039] A further technical solution further includes an optical fiber secondary amplification module for amplifying the signal light output by the optical fiber primary amplification module; The fiber optic secondary amplification module includes a third in-line isolator, a mode stripper, a fifth gain medium, a fourth beam combiner, and a fourth pump source connected in sequence; The input end of the third in-line isolator is connected to the signal output end of the third beam combiner; The fifth gain medium is an optical fiber doped with ytterbium ions; The fifth gain medium and the fourth pump source are used to cooperate to amplify the signal light output by the fiber optic primary amplification module; The fiber optic secondary amplification module further includes an output isolator, and the input end of the output isolator is connected to the signal output end of the fourth beam combiner.

[0040] The fiber optic secondary amplification module is used in cooperation with the fiber optic primary amplification module, has the same function as the fiber optic primary amplification module, and at the same time has unique functions, specifically as follows: The fiber optic secondary amplification module also has the function of realizing the amplification of the signal light power, further enabling the fiber laser to perform high-power laser output, so as to further meet various application scenarios that require high-energy laser, thereby further expanding the applicable range of the fiber laser; Different from the fiber optic primary amplification module, the fiber optic secondary amplification module has a mode stripper and an output isolator. The mode stripper can strip the excess pump light and a small amount of signal light in the optical fiber, retain more specific modes, ensure good specific mode output during this process, and at the same time reduce the thermal effect impact on the third in-line isolator caused by excessive pump light, which helps to improve the quality and purity of the optical signal; while the output isolator is mainly used to prevent the output laser from returning to the optical path, avoid damaging the optical path and optical devices, ensure the linear polarization state of the output light, and ensure the quality and stability of the output optical signal.

[0041] The fiber optic primary amplification module can be regarded as a pre-amplification stage system, and the fiber optic secondary amplification module can be regarded as a re-amplification stage system. The two cooperate to make the signal light power be amplified by multiple levels and multiple times.

[0042] This application only uses two-stage amplification modules to achieve high-power amplification, with fewer devices used, reducing the introduction of insertion loss and non-linearity, and enabling the fiber laser to have a smaller volume under the existing simple optical path structure, which is convenient for the miniaturization setting of the fiber laser.

[0043] A further technical solution further includes a first alarm module. The first alarm module includes a fuse provided on the fifth gain medium, and the fuse is used to give an alarm when the fifth gain medium fails.

[0044] The principle of using the fuse is prior art. Here, a specific usage method is supplemented as follows: Both ends of the fuse connector are respectively connected to the main control board (which can also be said to be the main control panel, referring to the above-mentioned control system) by wires to form a closed-loop circuit; when the fifth gain medium burns out and causes the fuse to blow, this closed-loop circuit then becomes an open circuit state; after receiving the open-circuit signal, the main control board cuts off the supply current of all pump sources (referring to each pump source), causing the pump sources to stop working, avoiding the aggravation of the fault degree of the fifth gain medium, and at the same time reducing the damage degree of other devices.

[0045] This application realizes the alarm function by means of a fuse, and protects the structure (which can also be said to be the device) within this application through the alarm, improving the safety of this application.

[0046] A further technical solution further includes a second alarm module. The second alarm module includes a photodiode disposed between the fourth beam combiner and the output isolator. The photodiode is used to give an alarm when the fifth gain medium fails.

[0047] In some embodiments, there is a high-refractive-index glue between the fourth beam combiner and the output isolator, and the photodiode is disposed at this position.

[0048] The principle of using the photodiode is prior art. Here, a specific usage method is supplemented as follows: The pins of the photodiode are connected to the above-mentioned main control board to form a closed-loop circuit; when this application is working normally, the photodiode receives light (which can also be said to be an optical signal), converts the light into an electrical signal, and then transmits the electrical signal to the main control board; when the main control board receives the electrical signal, it does not interfere with the operation of this application; when the fifth gain medium (which can also be other gain media) has a break point (which can also be other faults), there is no light refracted at the high-refractive-index glue, causing the photodiode to be unable to receive light, resulting in the main control board being unable to receive the electrical signal. At this time, the main control board defaults to triggering an alarm, and then cuts off the supply current of all pump sources, causing the pump sources to stop working, and timely reducing the damage degree of the devices within this application.

[0049] This application cooperates with the first alarm module to give an alarm through the second alarm module, adopting a dual alarm mechanism to improve the timeliness of the alarm, avoiding the situation that due to the failure of one of the alarm modules, the alarm cannot be given, and then the device is damaged or even a fire accident occurs. In addition, an alarm light can be used for prompting.

[0050] The dual alarm mechanism improves the value of this application in industrial applications.

[0051] It should be noted that, compared with other gain media, the probability of optical fiber breakage in the fifth gain medium of the optical fiber second-stage amplification module is the highest, because the laser power is the greatest here after two-stage amplification, resulting in a relatively large amount of energy borne by the fifth gain optical fiber. By arranging the first alarm module and the second alarm module in the optical fiber second-stage amplification module, the timeliness of alarm can be further improved.

[0052] In some embodiments, the above-mentioned combiners, gain media, reflection units, online isolators, mode strippers and output isolators are all polarization-maintaining devices to facilitate obtaining linearly polarized light.

[0053] Regarding the use of "first", "second", etc. in this article, it does not particularly refer to the meaning of order or sequence, nor is it used to limit this case. It is only used to distinguish components or operations described with the same technical terms.

[0054] Regarding the use of "connection" or "positioning" in this article, it can refer to two or more components or devices making direct physical contact with each other, or making indirect physical contact with each other. It can also refer to two or more components or devices operating or acting on each other.

[0055] Regarding the use of "comprising", "including", "having", etc. in this article, they are all open-ended terms, that is, they mean including but not limited to.

[0056] Regarding the terms used in this article, unless otherwise specified, they usually have the ordinary meanings of each term used in this field, in the context of this case and in the context of special content. Some terms used to describe this case will be discussed below or elsewhere in this specification to provide additional guidance to those skilled in the art regarding the description of this case.

[0057] Regarding the use of "front", "rear", "upper", "lower", "left", "right", etc. in this article, they are all directional terms. In this case, they are only used to illustrate the positional relationship between various structures, and are not used to limit the protection scheme of this case and the specific direction during actual implementation.

[0058] The working principle and advantages of the present invention are as follows: Instead of directly inputting the pump light of the first wavelength into the seed source module, this application converts the pump light of the first wavelength into the pump light of the second wavelength, and then inputs the pump light of the second wavelength into the seed source module. By reducing the population inversion degree of excited states, the gain of spontaneous emission is reduced, the risk of damage to the fiber laser caused by the spontaneous emission effect is reduced, and it helps to improve the stability of pulses and power.

[0059] This application reduces the risk of damage to the fiber laser, thereby reducing the equipment maintenance cost and the risk of production interruption, and further facilitating the wide application and performance improvement of the fiber laser in more fields.

[0060] This application improves the stability of pulses and power, enabling the laser to stably output high-quality laser light, which facilitates the laser to adapt to application scenarios such as precision machining and high-end scientific research that have extremely high requirements for laser stability.

[0061] This application improves the energy conversion efficiency of the laser by reducing the gain of spontaneous emission, enabling the energy input by the pump source to be efficiently converted into the required signal light energy and improving the energy utilization rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 It is a schematic structural diagram of the fiber laser according to an embodiment of the present invention; Figure 2 It is a schematic control diagram of the fiber laser according to an embodiment of the present invention; Figure 3 It is a schematic diagram of the power change of the signal light with the third wavelength output by the seed source module according to an embodiment of the present invention; Figure 4 It is a schematic diagram of the power change of the signal light output by the fiber first-stage amplification module according to an embodiment of the present invention; Figure 5 It is a schematic diagram of the power change of the signal light output by the fiber second-stage amplification module according to an embodiment of the present invention.

[0063] In the above drawings: 1. Seed pump source module; 11. First pump source; 12. First resonant cavity; 121. First gain medium; 122. First reflection unit; 1221. First high-reflection grating; 1222. First low-reflection grating; 123. First beam combiner; 124. First in-line isolator; 125. Third gain medium; 126. Second beam combiner; 127. Second pump source; 2. Seed source module; 21. Second resonant cavity; 211. Second gain medium; 212. Second reflection unit; 2121. Second high-reflection grating; 2122. Second low-reflection grating; 213. Control switch; 3. Fiber first-stage amplification module; 31. Second in-line isolator; 32. Mode matcher; 33. Fourth gain medium; 34. Third beam combiner; 35. Third pump source; 4. Fiber second-stage amplification module; 41. Third in-line isolator; 42. Mode stripper; 43. Fifth gain medium; 44. Fourth beam combiner; 45. Fourth pump source; 46. Output isolator; 5. First alarm module; 6. Second alarm module; 7. Control system. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0064] The present invention will be further described below in conjunction with the drawings and embodiments: Embodiment: The following will clearly explain this case with diagrams and detailed descriptions. After any person skilled in the art understands the embodiments of this case, they can make changes and modifications based on the technologies taught by this case without departing from the spirit and scope of this case.

[0065] The terms used in this document are only for describing specific embodiments and are not intended to limit the present case. Singular forms such as "a", "this", "that", "the", and "said", as used herein, also include the plural forms.

[0066] See Figures 1 - 5 , a high-repetition-rate polarization-maintaining ytterbium-doped fiber laser, including a seed pump source module 1 having a first gain medium 121 and a seed source module 2 having a second gain medium 211; Both the first gain medium 121 and the second gain medium 211 are fibers doped with ytterbium ions; The seed pump source module 1 includes a first pump source 11 that can output pump light of a first wavelength; The seed pump source module 1 is used to output pump light of a second wavelength to the seed source module 2; The seed source module 2 is used to absorb the pump light of the second wavelength and output signal light of a third wavelength; The first wavelength is less than or equal to 976 nm; The second wavelength is greater than 976 nm and less than 1100 nm; The third wavelength is greater than or equal to 1100 nm.

[0067] In this application, the pump light of the first wavelength is not directly input into the seed source module 2, but the pump light of the first wavelength is converted into the pump light of the second wavelength, and then the pump light of the second wavelength is input into the seed source module 2, reducing the gain of spontaneous emission by reducing the population inversion degree of excited states, reducing the risk of damage to the fiber laser caused by the spontaneous emission effect, and helping to improve the stability of pulses and power.

[0068] This application reduces the risk of damage to the fiber laser, thereby reducing the equipment maintenance cost and the risk of production interruption, and further facilitating the wide application and performance improvement of the fiber laser in more fields.

[0069] This application improves the stability of pulses and power, enabling the laser to stably output high-quality laser light, facilitating the laser to adapt to application scenarios such as precision machining and high-end scientific research that have extremely high requirements for laser stability.

[0070] This application improves the energy conversion efficiency of the laser by reducing the gain of spontaneous emission, enabling the energy input by the pump source to be efficiently converted into the required signal light energy and improving the energy utilization rate.

[0071] The fiber in this application can be set as polarization-maintaining (PM) gain fiber.

[0072] In some embodiments, the first pump source 11 is set as a 30W-VBG wavelength-locked 976nm pump source.

[0073] In some embodiments, the first gain medium 121 is a PM-10 / 130 Yb gain fiber.

[0074] In some embodiments, the second gain medium 211 is a PM-10 / 130 Yb gain fiber.

[0075] Such as Figure 2 , a control system 7 (such as a CPLD control system) is provided in the fiber laser, and the control logic refers to the relevant descriptions in the accompanying drawings and this application.

[0076] In this embodiment, the first wavelength is 976 nm; and / or, the second wavelength is 1030 nm; and / or, the third wavelength is 1100 nm.

[0077] It should be noted that taking the Yb gain fiber as the first gain medium 121 for illustration, currently, the mainstream pump light bands of the Yb gain fiber are 915 nm and 976 nm, and 976 nm is a band with a relatively high absorption intensity of Yb ions; setting the first wavelength to 976 nm enables the Yb ions to more effectively absorb the pump light energy, realize the transition from the ground state to the excited state, thereby improving the pump efficiency and enabling the Yb gain fiber to reach a relatively high gain level at a relatively low pump power.

[0078] It should also be noted that currently, the lasers emitted by the Yb gain fiber are 1030 nm and 1064 nm, and 1030 nm is a band with a relatively high emission intensity of the Yb gain fiber. Setting the second wavelength to 1030 nm enables the Yb gain fiber to more effectively convert the pump light energy into laser energy, realize a relatively high laser output power and optical-optical conversion efficiency, and has a relatively high degree of suppression of the spontaneous emission phenomenon.

[0079] In this embodiment, the seed pump source module 1 includes a first resonator 12, and the first gain medium 121 forms a part of the first resonator 12; The output end of the first pump source 11 is connected to the input end of the first resonator 12; The first resonator 12 is configured to absorb the pump light of the first wavelength and output the pump light of the second wavelength; The first resonator 12 includes a first reflection unit 122 for reflecting the pump light of the first wavelength.

[0080] The first reflection unit 122 includes a first high-reflection grating 1221 (which can also be said to be a high-reflective grating, such as a 1030 nm high-reflective grating, with a line width of 5 nm and a reflectivity range of 99% - 99.9%) and a first low-reflection grating 1222 (which can also be said to be a low-reflective grating, such as a 1030 nm low-reflective grating, with a line width of 5 nm and a reflectivity range of 20% - 30%).

[0081] The working principle of a specific embodiment of the first resonant cavity 12 is as follows: The first pump source 11 outputs pump light of the first wavelength into the first resonant cavity 12. Without considering repeated reflections, the pump light of the first wavelength sequentially passes through the first high-reflection grating 1221, the first gain medium 121, and the first low-reflection grating 1222, and finally forms pump light of the second wavelength; The first high-reflection grating 1221 feeds back light within a specific wavelength range into the first gain medium 121 to prepare for the subsequent light amplification process; When the light propagates in the first gain medium 121, it interacts with the particles in the population inversion state, forms oscillations within the first resonant cavity 12, and the light intensity gradually increases; The light emitted from the first gain medium 121 reaches the first low-reflection grating 1222. A part of the light is reflected back into the first gain medium 121 and continues to propagate in the first gain medium 121 and is further amplified, which helps to maintain the oscillation of the light within the first resonant cavity 12, and the other part of the light passes through the first low-reflection grating 1222 and is emitted as output light.

[0082] This embodiment clarifies the method of converting the pump light of the first wavelength into the pump light of the second wavelength, realizes the stable output of the pump light of the second wavelength, and thus realizes the stable operation of the fiber laser.

[0083] In this embodiment, the seed pump source module 1 further includes a first beam combiner 123, and the output end of the first pump source 11 is connected to the input end of the first resonant cavity 12 through the first beam combiner 123; And / or, the seed pump source module 1 further includes a first in-line isolator 124, and the output end of the first resonant cavity 12 is connected to the input end of the first in-line isolator 124; And / or, the seed pump source module 1 further includes a third gain medium 125, a second beam combiner 126, and a second pump source 127. The third gain medium 125 is an ytterbium-doped fiber. The first resonant cavity 12, the third gain medium 125, the second beam combiner 126, and the second pump source 127 are connected in sequence. The third gain medium 125 and the second pump source 127 are used to cooperate to amplify the pump light of the second wavelength.

[0084] The first beam combiner 123 can combine the pump light output by multiple pump sources, so as to provide sufficient pump light for the fiber laser and meet the diverse requirements of the fiber laser for the power of the output light. The first pump source 11 may include multiple sub-pump sources, and the same applies to the following second pump source 127 and the like.

[0085] The first in-line isolator 124 is applied here to minimize the reverse propagation of light after leaving the first resonator 12, thereby improving the stability and reliability of the fiber laser. In some embodiments, the first in-line isolator 124 is disposed between the first resonator 12 and the third gain medium 125, and the output end of the first in-line isolator 124 is connected to the input end of the third gain medium 125.

[0086] Before the seed pump source module 1 outputs the pump light of the second wavelength to the seed source module 2, the third gain medium 125 and the second pump source 127 cooperate to amplify the pump light of the second wavelength, so as to provide sufficient pump light for the output of the signal light of the third wavelength by the second resonator 21 in the seed source module 2, meeting the stable output requirements of the fiber laser for light of a specific wavelength.

[0087] In some embodiments, the first beam combiner 123 is configured as a PM(2 + 1)x1 beam combiner.

[0088] In some embodiments, the first in-line isolator 124 is configured as a 10W in-line isolator.

[0089] In some embodiments, the third gain medium 125 is configured as a PM-10 / 130 Yb gain fiber.

[0090] In some embodiments, the second beam combiner 126 is configured as a reverse PM(2 + 1)x1 beam combiner.

[0091] In some embodiments, the second pump source 127 is configured as a 30W-VBG wavelength-locked 976nm pump source.

[0092] In this embodiment, the seed source module 2 further includes a second resonator 21, and the second gain medium 211 forms part of the second resonator 21; The output end of the seed pump source module 1 is connected to the input end of the second resonator 21; The second resonator 21 is configured to absorb the pump light of the second wavelength and output the signal light of the third wavelength; The second resonator 21 includes a second reflection unit 212 configured to reflect the pump light of the second wavelength.

[0093] The second reflection unit 212 includes a second high-reflection grating 2121 (such as a 1100nm high-reflection grating with a line width of 5nm and a reflectivity range of 99%-99.9%) and a second low-reflection grating 2122 (such as a 1100nm low-reflection grating with a line width of 5nm and a reflectivity range of 65%-70%).

[0094] The working principle of a specific embodiment of the second resonant cavity 21 is as follows: The seed pump source module 1 outputs pump light of a second wavelength into the second resonant cavity 21. Without considering repeated reflections, the pump light of the second wavelength sequentially passes through the second high-reflection grating 2121, the second gain medium 211, and the second low-reflection grating 2122, and finally forms signal light of a third wavelength. The second high-reflection grating 2121 feeds back light within a specific wavelength range into the second gain medium 211 to prepare for the subsequent optical amplification process. When the light propagates in the second gain medium 211, it interacts with the particles in the population inversion state, forms oscillations within the second resonant cavity 21, and the light intensity gradually increases. The light emitted from the second gain medium 211 reaches the second low-reflection grating 2122. A part of the light is reflected back into the second gain medium 211 and continues to propagate in the second gain medium 211 and is further amplified, which helps to maintain the oscillation of the light within the second resonant cavity 21. Another part of the light passes through the second low-reflection grating 2122 and is emitted as output light.

[0095] The seed source module 2 converts the pump light of the second wavelength into signal light of the third wavelength through the second resonant cavity 21 to meet the output requirements of the fiber laser for light of a specific wavelength.

[0096] In some embodiments, before the pump light of the second wavelength enters the second resonant cavity 21, it first passes through a spot of glue with refractive index, the purpose of which is to filter out the pump light.

[0097] In this embodiment, the seed source module 2 further includes a control switch 213 disposed within the second resonant cavity 21.

[0098] The control switch 213 can control the output of the signal light of the third wavelength.

[0099] In some embodiments, the control switch 213 is disposed between the second gain medium 211 and the second low-reflection grating 2122, which can better achieve population inversion energy storage.

[0100] In some embodiments, the control switch 213 is set as an acousto-optic Q drive switch. The Q drive gives a high-frequency radio frequency signal to the acousto-optic Q switch to enable the laser to achieve high-repetition rate pulsed output. The control switch 213 can be set as part of the second resonant cavity 21 or as a structure that does not belong to the second resonant cavity 21.

[0101] In this embodiment, it also includes an optical fiber primary amplification module 3, which is used to amplify the signal light of the third wavelength; The optical fiber primary amplification module 3 comprises a second online isolator 31, a mode matcher 32, a fourth gain medium 33, a third beam combiner 34 and a third pump source 35 which are connected in sequence; The input end of the second online isolator 31 is connected to the output end of the seed source module 2; The fourth gain medium 33 is an optical fiber doped with ytterbium ions; the diameter of the optical fiber in the fourth gain medium 33 is greater than the diameter of the optical fiber in the second gain medium 211; The fourth gain medium 33 and the third pump source 35 are used to cooperate to amplify the signal light of the third wavelength.

[0102] The actual optical amplification structure in the optical fiber primary amplification module 3 is the fourth gain medium 33 and the third pump source 35. The fourth gain medium 33 and the third pump source 35 can cooperate to achieve power amplification of the signal light of the third wavelength, thereby obtaining a higher-power laser output, preparing for further increasing the laser power in the future, so as to meet various application scenarios requiring high-energy lasers and expand the scope of application of optical fiber lasers.

[0103] In the optical fiber primary amplifier module 3, the second in-line isolator 31 is used to prevent the light from propagating in the reverse direction after entering the optical fiber primary amplifier module 3, thereby avoiding damage to the device and improving the stability and reliability of the optical fiber laser. In some embodiments, the second in-line isolator 31 is disposed between the second low-reflection grating 2122 and the mode matcher 32.

[0104] The purpose of the third beam combiner 34 is similar to the description of the first beam combiner 123 .

[0105] The diameter of the optical fiber in the fourth gain medium 33 is greater than the diameter of the optical fiber in the second gain medium 211. It can be considered that the optical fiber in the second gain medium 211 is thinner, while the optical fiber in the fourth gain medium 33 is thicker. Using an optical fiber with a thicker core diameter can increase the nonlinear threshold, thereby suppressing the generation of nonlinearity.

[0106] Since the diameter of the optical fiber in the fourth gain medium 33 is different from the diameter of the optical fiber in the second gain medium 211 , the mode matcher 32 is arranged based on this to achieve efficient coupling and transmission of light between the two optical fibers.

[0107] It should be emphasized that the structures in the fiber first-stage amplification module 3 have a synergistic effect. The fourth gain medium 33 and the third pump source 35 cooperate to amplify the signal light of the third wavelength, achieving the purpose of optical power amplification, which will cause the generation of nonlinear optical effects. Based on this, a thicker optical fiber in the fourth gain medium 33 is used in cooperation with the mode matcher 32 to solve this problem, ensuring that the fiber laser can stably output high-power laser.

[0108] Nonlinear optical effects will cause some problems, such as the laser output power no longer increasing linearly with the pump power, which limits the development of fiber lasers in the high-power direction. This is an existing influence and will not be elaborated here.

[0109] In some embodiments, the second in-line isolator 31 is set as a narrow-band 10W in-line isolator. The in-line isolator with a narrower bandwidth can play a role in filtering and narrowing the spectrum, thereby suppressing the re-amplification of nonlinearity.

[0110] In some embodiments, the mode matcher 32 is set as an MFA mode matcher 32.

[0111] In some embodiments, the fourth gain medium 33 is set as a PM-30 / 250YB gain fiber.

[0112] In some embodiments, the third beam combiner 34 is set as a reverse PM (2 + 1) x1 beam combiner.

[0113] In some embodiments, the third pump source 35 is set as a 30W-VBG wavelength-locked 976nm pump source.

[0114] In this embodiment, it further includes a fiber second-stage amplification module 4 for amplifying the signal light output by the fiber first-stage amplification module 3; The fiber second-stage amplification module 4 includes a third in-line isolator 41, a stripping module 42, a fifth gain medium 43, a fourth beam combiner 44 and a fourth pump source 45 connected in sequence; The input end of the third in-line isolator 41 is connected to the (signal) output end of the third beam combiner 34; The fifth gain medium 43 is an optical fiber doped with ytterbium ions; The fifth gain medium 43 and the fourth pump source 45 are used to cooperate to amplify the signal light output by the fiber first-stage amplification module 3; The fiber second-stage amplification module 4 further includes an output isolator 46, and the input end of the output isolator 46 is connected to the (signal) output end of the fourth beam combiner 44.

[0115] The fiber second-stage amplification module 4 is used in cooperation with the fiber first-stage amplification module 3, having the same function as the fiber first-stage amplification module 3 and also having unique functions, as follows: The fiber optic secondary amplification module 4 also plays a role in amplifying the signal optical power, further enabling the fiber laser to output high-power laser, so as to further meet various application scenarios that require high-energy laser, thereby further expanding the applicable range of the fiber laser; Different from the fiber optic primary amplification module 3, the fiber optic secondary amplification module 4 has a mode stripper 42 and an output isolator 46. The mode stripper 42 can strip the excess pump light and a small amount of signal light in the optical fiber, retaining more specific modes, ensuring good output of specific modes in this process, and at the same time reducing the thermal effect on the third in-line isolator 41 caused by excessive pump light, which helps to improve the quality and purity of the optical signal; while the output isolator 46 is mainly used to prevent the output laser from returning to the optical path, avoiding damaging the optical path and optical devices, ensuring the linear polarization state of the output light, and ensuring the quality and stability of the output optical signal.

[0116] The fiber optic primary amplification module 3 can be regarded as a pre-amplification stage system, and the fiber optic secondary amplification module 4 can be regarded as a re-amplification stage system. The two cooperate to achieve multi-stage and multi-fold amplification of the signal optical power.

[0117] This application only uses two-stage amplification modules to achieve high-power amplification, with fewer devices used, reducing the introduction of insertion loss and non-linearity, and enabling the fiber laser to have a smaller volume under the existing simple optical path structure, facilitating the miniaturization setting of the fiber laser.

[0118] In some embodiments, the third in-line isolator 41 is set as a 30W narrow-band in-line isolator.

[0119] In some embodiments, the mode stripper 42 is set as a PM-mode stripper 42.

[0120] In some embodiments, the fifth gain medium 43 is set as a PM-30 / 250 gain fiber.

[0121] In some embodiments, the fourth beam combiner 44 is set as a reverse (6 + 1) x1 beam combiner.

[0122] In some embodiments, the fourth pump source 45 is set as a 240W-VBG wavelength-locked 976nm pump source.

[0123] In some embodiments, the output isolator 46 is set as a PM-output isolator 46.

[0124] See Figures 3 - 5 , the power of the signal light gradually increases, and the actual power size is adjusted according to requirements. The power in the figure is only for reference to help understanding. Figure 3 For the signal light corresponding to the third wavelength, this application reduces the spontaneous emission effect, improves the optical-optical conversion efficiency, and at the same time improves the power and pulse stability of the signal light of the third wavelength. ForFigure 3 As can be seen from the power curve in the figure, the power stability is < 5%, the power fluctuation is small, and the curve is relatively smooth and stable. For Figure 4 As can be learned from the figure, the power stability is 1.66%, the power fluctuation is small, and the power curve is relatively smooth and stable. For Figure 5 As can be seen from the figure, the power stability is 1.22%, the power curve is relatively smooth and stable, and the output pulses are also relatively stable at this time. Since the present application can reduce the spontaneous emission effect, the adverse effect of ASE on the fiber laser when achieving high-power output can be weakened.

[0125] In this embodiment, a first alarm module 5 is further included. The first alarm module 5 includes a fuse disposed on the fifth gain medium 43, and the fuse is used to alarm when the fifth gain medium 43 fails.

[0126] The principle of using the fuse is prior art. Here, a specific usage method is supplemented as follows: both ends of the fuse connector are respectively connected to the main control board by wires to form a closed-loop circuit; when the fifth gain medium 43 burns out and causes the fuse to blow, this closed-loop circuit becomes an open state at this time; after receiving the open signal, the main control board cuts off the supply current of all pump sources (referring to each pump source), stops the pump sources from working, avoids the aggravation of the failure degree of the fifth gain medium 43, and at the same time can reduce the damage degree of other devices.

[0127] The present application realizes the alarm function by means of the fuse, and protects the internal structure (or devices) of the present application through the alarm, improving the safety of the present application.

[0128] In this embodiment, a second alarm module 6 is further included. The second alarm module 6 includes a photosensitive diode disposed between the fourth beam combiner 44 and the output isolator 46, and the photosensitive diode is used to alarm when the fifth gain medium 43 fails.

[0129] In some embodiments, there is a high refractive index glue between the fourth beam combiner 44 and the output isolator 46, and the photosensitive diode is disposed at this position.

[0130] The principle of using a photodiode is prior art. Here, a specific usage method is supplemented as follows: The pins of the photodiode are connected to the above-mentioned main control board to form a closed-loop circuit; when the present application is working properly, the photodiode receives light (which can also be said to be an optical signal), converts the light into an electrical signal, and then transmits the electrical signal to the main control board; when the main control board receives the electrical signal, it does not interfere with the operation of the present application; when a break (which can also be other faults) occurs in the fifth gain medium 43 (which can also be other gain media), no light is refracted at the high-refractive-index glue, so that the photodiode cannot receive light, resulting in the main control board not receiving the electrical signal. At this time, the main control board defaults to triggering an alarm, and then disconnects the supply current of all pump sources, causing the pump sources to stop working, and timely reducing the damage degree of the components in the present application.

[0131] The present application cooperates with the first alarm module 5 through the second alarm module 6 to give an alarm, and adopts a dual alarm mechanism to improve the timeliness of the alarm, avoiding the inability to give an alarm due to a failure of one of the alarm modules, which may cause damage to the components or even lead to a fire accident. In addition, an alarm light can be used for prompting.

[0132] The dual alarm mechanism improves the value of the present application in industrial applications.

[0133] It should be noted that compared with other gain media, the probability of the fifth gain medium 43 in the fiber second-stage amplification module 4 having a fiber break is the highest, because the laser power is the largest here after two-stage amplification, resulting in the fifth gain fiber bearing a large amount of energy. By arranging the first alarm module 5 and the second alarm module 6 in the fiber second-stage amplification module 4, the timeliness of the alarm can be further improved.

[0134] In some embodiments, the above-mentioned beam combiners, gain media, reflection units, in-line isolators, mode strippers 42, and output isolators 46 are all polarization-maintaining devices to facilitate obtaining linearly polarized light.

[0135] The above embodiments are only used to illustrate the technical concept and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and it should not be used to limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims

1. High-repetition-rate polarization-maintaining ytterbium-doped fiber laser, characterized in that: It includes a seed pump source module (1) and a seed source module (2); The seed pump source module (1) includes: A first pump source (11) for outputting pump light of a first wavelength; A first resonant cavity (12) including a first gain medium (121) and a first reflection unit (122) for reflecting the pump light of the first wavelength, for absorbing the pump light of the first wavelength and outputting pump light of a second wavelength; The seed source module (2) includes: A second resonant cavity (21) including a second gain medium (211) and a second reflection unit (212) for reflecting the pump light of the second wavelength, for absorbing the pump light of the second wavelength and outputting signal light of a third wavelength; Both the first gain medium (121) and the second gain medium (211) are ytterbium-doped fibers; The first wavelength is less than or equal to 976 nm; The second wavelength is greater than 976 nm and less than 1100 nm; The third wavelength is greater than or equal to 1100 nm.

2. The polarization-maintaining ytterbium-doped fiber laser with high repetition rate according to claim 1, characterized in that: The first wavelength is 976 nm; And / or, the second wavelength is 1030 nm; And / or, the third wavelength is 1100 nm.

3. The polarization-maintaining ytterbium-doped fiber laser with high repetition rate according to claim 1, characterized in that: The seed pump source module (1) further includes a first beam combiner (123), and the output end of the first pump source (11) is connected to the input end of the first resonant cavity (12) through the first beam combiner (123); And / or, the seed pump source module (1) further includes a first in-line isolator (124), and the output end of the first resonant cavity (12) is connected to the input end of the first in-line isolator (124); And / or, the seed pump source module (1) further includes a third gain medium (125), a second beam combiner (126) and a second pump source (127), the third gain medium (125) is an ytterbium-doped fiber, the first resonant cavity (12), the third gain medium (125), the second beam combiner (126) and the second pump source (127) are connected in sequence, and the third gain medium (125) and the second pump source (127) are used to cooperate to amplify the pump light of the second wavelength.

4. The polarization-maintaining ytterbium-doped fiber laser with high repetition rate according to claim 1, characterized in that: The seed source module (2) further includes a control switch (213) disposed in the second resonant cavity (21).

5. The polarization-maintaining ytterbium-doped fiber laser with high repetition rate according to any one of claims 1-4, characterized in that: It further includes an optical fiber primary amplification module (3) for amplifying the signal light of the third wavelength; The optical fiber primary amplification module (3) includes a second in-line isolator (31), a mode matcher (32), a fourth gain medium (33), a third beam combiner (34) and a third pump source (35) connected in sequence; The input end of the second in-line isolator (31) is connected to the output end of the seed source module (2); The fourth gain medium (33) is an ytterbium-doped fiber; the diameter of the fiber in the fourth gain medium (33) is greater than the diameter of the fiber in the second gain medium (211); The fourth gain medium (33) and the third pump source (35) are used to cooperate to amplify the signal light of the third wavelength.

6. The polarization-maintaining ytterbium-doped fiber laser with high repetition rate according to claim 5, characterized in that: It further includes an optical fiber secondary amplification module (4) for amplifying the signal light output by the optical fiber primary amplification module (3); The optical fiber secondary amplification module (4) includes a third in-line isolator (41), a mode stripper (42), a fifth gain medium (43), a fourth beam combiner (44) and a fourth pump source (45) connected in sequence; The input end of the third in-line isolator (41) is connected to the signal output end of the third beam combiner (34); The fifth gain medium (43) is an optical fiber doped with ytterbium ions; The fifth gain medium (43) and the fourth pump source (45) are used to cooperate to amplify the signal light output by the optical fiber primary amplification module (3); The optical fiber secondary amplification module (4) further includes an output isolator (46), and the input end of the output isolator (46) is connected to the signal output end of the fourth beam combiner (44).

7. The polarization-maintaining ytterbium-doped fiber laser with high repetition rate according to claim 6, wherein: It further includes a first alarm module (5), and the first alarm module (5) includes a fuse provided on the fifth gain medium (43), and the fuse is used to give an alarm when the fifth gain medium (43) fails.

8. The polarization-maintaining ytterbium-doped fiber laser with high repetition rate according to claim 7, wherein: It further includes a second alarm module (6), and the second alarm module (6) includes a photodiode provided between the fourth beam combiner (44) and the output isolator (46), and the photodiode is used to give an alarm when the fifth gain medium (43) fails.

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