A mode-locked fiber laser system based on an online coupling method

Abstract

The application discloses a mode-locked fiber laser system based on an online coupling method, wherein an online coupling module is connected with a wavelength division multiplexing beam splitter, a fifth optical fiber, a gain optical fiber and a sixth optical fiber are sequentially fused, the fifth optical fiber is connected with the wavelength division multiplexing beam splitter, the wavelength division multiplexing beam splitter is connected with a first optical fiber collimator, output light of the first optical fiber collimator sequentially passes through a first polarization beam splitter, a Faraday rotator, a first wave plate, a second polarization beam splitter, a second wave plate, a mirror and a sixth optical fiber collimator, output light of the first polarization beam splitter passes through the first optical fiber collimator, a second optical fiber collimator and a third optical fiber collimator, and output light of the second polarization beam splitter passes through a fourth optical fiber collimator and a fifth optical fiber collimator. The application simplifies a coupling structure, reduces processing difficulty and maintenance cost, improves a repetition frequency of a fiber mode-locked laser, and outputs high-quality in-cavity pulses under high repetition frequency.

Description

Technical Field

[0001] This invention relates to the field of ultrashort pulse laser technology, and more specifically, to a mode-locked fiber laser system based on an online coupling method. Background Technology

[0002] Over the past twenty-five years, significant progress has been made in both the theory and experimentation of mode-locked fiber lasers, leading to numerous applications such as materials processing, precision ranging, trace gas measurement, quantum information and quantum computing, frequency metrology, and timing and synchronization. Currently, in the field of mode-locked fiber lasers, the use of nonlinear amplified ring mirror (NALM) technology to generate ultrashort pulses is one of the most popular methods. Its working principle involves generating two beams of light propagating in opposite directions within an optical fiber loop, interfering with each other at a beam splitter, and utilizing the different nonlinear phase shifts accumulated by the two beams in the loop to control the transmittance of the beam splitter for light of different intensities, thereby achieving saturable absorption characteristics.

[0003] Fiber lasers based on nonlinear amplifying ring mirror mode-locking currently face many challenges. Research shows that pulse quality varies at different locations within the laser, with the highest quality pulses occurring within the ring. However, adding fiber optic devices to split the output pulses within the ring is detrimental to high-repetition-rate laser fabrication. Regarding collimator coupling in laser systems, fiber fusion splicing and collimator coupling operations are interleaved, resulting in cumbersome procedures, poor laser fabrication consistency, and the potential for fiber damage from the coupling adjustment mechanisms. In assembled high-repetition-rate mode-locked fiber lasers, the fiber fusion splicing limit is reached. If collimator coupling decreases, maintenance requires disconnecting the fiber optic devices and connecting to an external coupling system for recoupling, potentially rendering all fiber optic devices in the system unusable. In traditional collimator coupling methods, fiber splicing is limited by collimator position and the need to place the fiber fusion splicer within the loop, requiring additional fiber to be reserved during splicing, which is detrimental to increasing the repetition rate.

[0004] Therefore, how to design a mode-locked fiber laser system based on an online coupling method, simplify the coupling structure, reduce the processing difficulty and maintenance cost, increase the repetition frequency of the fiber mode-locked laser, and output high-quality pulses within the loop at a high repetition frequency has become an important issue that urgently needs to be addressed. Summary of the Invention

[0005] The purpose of this invention is to provide a mode-locked fiber laser system based on an online coupling method to overcome the shortcomings of the prior art.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A mode-locked fiber laser system based on an online coupling method includes an online coupling module, a wavelength division multiplexing beam splitter, a fifth fiber, a gain fiber, a sixth fiber, a fourth fiber, a first fiber collimator, a second fiber collimator, a first polarization beam splitter, a Faraday rotator, a first waveplate, a second polarization beam splitter, a second waveplate, a mirror, a third fiber collimator, a fourth fiber collimator, a fifth fiber collimator, and a sixth fiber collimator. The online coupling module is connected to the wavelength division multiplexing beam splitter. The fifth fiber, the gain fiber, and the sixth fiber collimator... The fibers are spliced ​​sequentially. The fifth fiber is connected to a wavelength division multiplexing beamsplitter. The wavelength division multiplexing beamsplitter is connected to the first fiber collimator via a fourth fiber. The output light of the first fiber collimator sequentially passes through a first polarization beamsplitter, a Faraday rotator, a first waveplate, a second polarization beamsplitter, a second waveplate, a mirror, and a sixth fiber collimator. The output light of the first polarization beamsplitter passes through a first fiber collimator, a second fiber collimator, and a third fiber collimator. The output light of the second polarization beamsplitter passes through a fourth fiber collimator and a fifth fiber collimator.

[0008] Further, the online coupling module includes a third port, a thirteenth optical fiber, a pump light source, a second port, a fifteenth optical fiber, a first optical fiber circulator, an eleventh optical fiber, a first light source, a fourteenth optical fiber, a first power meter, a first port, a seventeenth optical fiber, a second optical fiber circulator, a twelfth optical fiber, a second light source, a sixteenth optical fiber, and a second power meter. The first port, the second port, and the third port are connected to a wavelength division multiplexing beam splitter. The third port, the thirteenth optical fiber, and the pump light source are connected in sequence. The second port, the fifteenth optical fiber, the first optical fiber circulator, the eleventh optical fiber, and the first light source are connected in sequence. The first optical fiber circulator is connected to the first power meter via the fourteenth optical fiber. The first port, the seventeenth optical fiber, the second optical fiber circulator, the twelfth optical fiber, and the second light source are connected in sequence. The second optical fiber circulator is connected to the second power meter via the sixteenth optical fiber.

[0009] Furthermore, the wavelength division multiplexing beam splitter includes a first optical fiber, a second optical fiber, a third optical fiber, a fourth optical fiber, a fifth optical fiber, an optical fiber coupler, and an optical fiber wavelength division multiplexer. The optical fiber coupler is connected to the optical fiber wavelength division multiplexer via an eighteenth optical fiber. The first, second, and fourth optical fibers are connected to the optical fiber coupler, and the third and fifth optical fibers are connected to the optical fiber wavelength division multiplexer. When light is input into the fifth optical fiber, light is output from the fourth and second optical fibers. When light is input into the second optical fiber, light is output from the first and fifth optical fibers. When pump light is input into the third optical fiber, it is reflected by the wavelength division multiplexing beam splitter and enters the fifth optical fiber.

[0010] Further, the wavelength division multiplexing (WDM) beamsplitter includes a first optical fiber, a second optical fiber, a third optical fiber, a fourth optical fiber, a fifth optical fiber, a seventh optical fiber collimator, an eighth optical fiber collimator, a ninth optical fiber collimator, a third polarization beamsplitter, a third waveplate, a fourth polarization beamsplitter, and a WDM collimator. The output light from the ninth optical fiber collimator sequentially passes through the third polarization beamsplitter, the third waveplate, the fourth polarization beamsplitter, and the WDM collimator. The output light from the third polarization beamsplitter passes through the ninth and seventh optical fiber collimators. The output light from the fourth polarization beamsplitter passes through the eighth and WDM collimators. The first optical fiber is connected to the eighth optical fiber collimator, the second optical fiber is connected to the seventh optical fiber collimator, the third and fifth optical fibers are connected to the WDM collimator, and the fourth optical fiber is connected to the ninth optical fiber collimator. When light is input into the fifth optical fiber, light is output from the fourth and second optical fibers. When light is input into the second optical fiber, light is output from the first and fifth optical fibers. When pump light is input into the third optical fiber, it is reflected by the WDM beamsplitter and enters the fifth optical fiber.

[0011] Further, the wavelength division multiplexing (WDM) beamsplitter includes a first optical fiber, a second optical fiber, a third optical fiber, a fourth optical fiber, a fifth optical fiber, a seventh optical fiber collimator, an eighth optical fiber collimator, a ninth optical fiber collimator, a third polarization beamsplitter, a fourth polarization beamsplitter, and a WDM collimator. The output light from the ninth optical fiber collimator sequentially passes through the third polarization beamsplitter, the fourth polarization beamsplitter, and the WDM collimator. The output light from the third polarization beamsplitter passes through the ninth and seventh optical fiber collimators. The output light from the fourth polarization beamsplitter passes through the eighth optical fiber collimator and the WDM collimator. The first optical fiber is connected to the eighth optical fiber collimator, the second optical fiber is connected to the seventh optical fiber collimator, the third and fifth optical fibers are connected to the WDM collimator, and the fourth optical fiber is connected to the ninth optical fiber collimator. When light is input into the fifth optical fiber, light is output from the fourth and second optical fibers. When light is input into the second optical fiber, light is output from the first and fifth optical fibers. When pump light is input into the third optical fiber, it is reflected by the WDM beamsplitter and enters the fifth optical fiber.

[0012] Furthermore, the online coupling method of the system is as follows: turn on the second light source, adjust the angle and displacement of the first fiber collimator to maximize the reading of the second power meter, and fix the first fiber collimator; turn off the second light source, turn on the first light source, adjust the angle and displacement of the second fiber collimator to maximize the reading of the first power meter; turn off the first light source, turn on the pump light source, adjust the angle and displacement of the second fiber collimator to maximize the reading of the second power meter, and fix the second fiber collimator.

[0013] Furthermore, the online coupling method of the system is as follows: turn on the second light source, adjust the angle and displacement of the first fiber collimator to maximize the reading of the second power meter, and fix the first fiber collimator; adjust the angle and displacement of the third fiber collimator to maximize the output optical power of the seventh fiber and fix it; turn on the first light source, adjust the angle and displacement of the second fiber collimator to maximize the overlap of the two light spots output by the first polarization beam splitter or maximize the output optical power of the seventh fiber, and fix the second fiber collimator.

[0014] Furthermore, the online coupling method of this system is as follows: adjusting the angle and displacement of the fourth fiber collimator and the fifth fiber collimator to maximize and fix the coupling efficiency of the fourth fiber collimator and the fifth fiber collimator; turning on the second light source, adjusting the angle and displacement of the first fiber collimator to maximize the output optical power of the ninth fiber, and fixing the first fiber collimator; turning off the second light source, turning on the first light source, adjusting the angle and displacement of the second fiber collimator to maximize the output optical power of the eighth fiber, and fixing the second fiber collimator.

[0015] Furthermore, the online coupling method of the system is as follows: turn on the second light source, adjust the angle and displacement of the first fiber collimator to maximize the output optical power of the tenth fiber, and fix the first fiber collimator; turn off the second light source, turn on the first light source, adjust the angle and displacement of the second fiber collimator to maximize the output optical power of the tenth fiber, and fix the second fiber collimator.

[0016] Compared with existing technologies, the advantages of this invention are as follows: The online coupling method in this invention is based on the laser system itself, allowing for online adjustment of the collimator coupling without the aid of external equipment. Furthermore, the online coupling method makes fiber splicing and collimator coupling two independent steps, simplifying the manufacturing process. Splicing all fibers first helps to increase the repetition rate. This is because in traditional coupling methods, fiber splicing is limited by the collimator position, requiring the fiber fusion splicer to be placed within the loop, necessitating the reservation of a long fiber length. In the online coupling method, splicing all fibers involves linearly fusing all fiber components, eliminating the limitations of traditional methods and allowing for shorter cavity lengths. While maintaining a high repetition rate, the wavelength division multiplexing beam splitter's pigtail can output high-quality pulses within the loop. When the collimator coupling efficiency of the laser system decreases, only the collimator needs to be adjusted to improve coupling efficiency; there is no need to disconnect the fiber components and connect to an external coupling system for recoupling, avoiding the problem of fiber component failure. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of a mode-locked fiber laser system based on an online coupling method, provided in an embodiment of the present invention.

[0019] Figure 2 This is a schematic diagram of the online coupling module in a mode-locked fiber laser system based on an online coupling method, provided in an embodiment of the present invention.

[0020] Figure 3 This is a schematic diagram of the wavelength division multiplexing beam splitter in a mode-locked fiber laser system based on an online coupling method, provided as an embodiment of the present invention.

[0021] Figure 4 This is a schematic diagram of the wavelength division multiplexing beam splitter in a mode-locked fiber laser system based on an online coupling method, provided as an embodiment of the present invention.

[0022] Figure 5 This is a schematic diagram of the wavelength division multiplexing beam splitter in a mode-locked fiber laser system based on an online coupling method, provided as an embodiment of the present invention.

[0023] In the diagram: 1. In-line coupling module; 2. First port; 3. First fiber; 4. Second port; 5. Fourth fiber; 6. First fiber collimator; 7. First polarization beam splitter; 8. Seventh fiber; 9. Third fiber collimator; 10. Eighth fiber; 11. Fifth fiber collimator; 12. Second waveplate; 13. Mirror; 14. Third port; 15. Second fiber; 16. Third fiber; 17. Wavelength division multiplexing beam splitter; 18. Fifth fiber; 19. Gain fiber; 20. Sixth fiber; 21. Second fiber collimator; 22. Faraday rotator; 23. First waveplate; 24. Ninth fiber; 25. Fourth fiber collimator; 26. Second polarization beam splitter; 27. Sixth fiber collimator ; 28. Tenth fiber; 29. ​​First light source; 30. Second light source; 31. Twelfth fiber; 32. Second fiber circulator; 33. Seventeenth fiber; 34. Sixteenth fiber; 35. Fifteenth fiber; 36. Second power meter; 37. Eleventh fiber; 38. Pump light source; 39. Thirteenth fiber; 40. First fiber circulator; 41. Fourteenth fiber; 42. First power meter; 43. Fiber coupler; 44. Fiber wavelength division multiplexer; 45. Eighteenth fiber; 46. Seventh fiber collimator; 47. Eighth fiber collimator; 48. Ninth fiber collimator; 49. Third polarization beam splitter; 50. Third waveplate; 51. Fourth polarization beam splitter; 52. Wavelength division multiplexing collimator. Detailed Implementation

[0024] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0025] See Figure 1As shown, this embodiment discloses a mode-locked fiber laser system based on an online coupling method, including an online coupling module 1, a wavelength division multiplexing beam splitter 17, a fifth fiber 18, a gain fiber 19, a sixth fiber 20, a fourth fiber 5, a first fiber collimator 6, a second fiber collimator 21, a first polarization beam splitter 7, a Faraday rotator 22, a first waveplate 23, a second polarization beam splitter 26, a second waveplate 12, a mirror 13, a third fiber collimator 9, a fourth fiber collimator 25, a fifth fiber collimator 11, and a sixth fiber collimator 27. The online coupling module 1 is connected to the wavelength division multiplexing beam splitter 17, and the fifth fiber 18, gain fiber 19, and gain fiber 20 are connected to the Faraday rotator 17. Fiber 19 and the sixth fiber 20 are fused together in sequence. The fifth fiber is connected to the wavelength division multiplexing beam splitter 17. The wavelength division multiplexing beam splitter 17 is connected to the first fiber collimator 6 through the fourth fiber 5. The output light of the first fiber collimator 6 passes sequentially through the first polarization beam splitter 7, the Faraday rotator 22, the first waveplate 23, the second polarization beam splitter 26, the second waveplate 12, the reflector 13, and the sixth fiber collimator 27. The output light of the first polarization beam splitter 7 passes through the first fiber collimator 6, the second fiber collimator 21, and the third fiber collimator 9. The output light of the second polarization beam splitter 26 passes through the fourth fiber collimator 25 and the fifth fiber collimator 11.

[0026] See Figure 2 As shown, the online coupling module 1 includes a third port 14, a thirteenth optical fiber 39, a pump light source 38, a second port 4, a fifteenth optical fiber 35, a first optical fiber circulator 40, an eleventh optical fiber 37, a first light source 29, a fourteenth optical fiber 41, a first power meter 42, a first port 2, a seventeenth optical fiber 33, a second optical fiber circulator 32, a twelfth optical fiber 31, a second light source 30, a sixteenth optical fiber 34, and a second power meter 36. The first port 2, the second port 4, and the third port 14 are connected to the wavelength division multiplexing beam splitter 17. The third port 14, the thirteenth fiber 39, and the pump light source 38 are connected in sequence; the second port 4, the fifteenth fiber 35, the first fiber circulator 40, the eleventh fiber 37, and the first light source 29 are connected in sequence; the first fiber circulator 40 and the first power meter 42 are connected through the fourteenth fiber 41; the first port 2, the seventeenth fiber 33, the second fiber circulator 32, the twelfth fiber 31, and the second light source 30 are connected in sequence; the second fiber circulator 32 and the second power meter 36 are connected through the sixteenth fiber 34.

[0027] See Figure 3As shown, the first structure of the wavelength division multiplexing beam splitter 17 includes a first optical fiber 3, a second optical fiber 15, a third optical fiber 16, a fourth optical fiber 5, a fifth optical fiber 18, an optical fiber coupler 43, and an optical fiber wavelength division multiplexer 44. The optical fiber coupler 43 and the optical fiber wavelength division multiplexer 44 are connected through an eighteenth optical fiber 45. The first optical fiber 3, the second optical fiber 15, and the fourth optical fiber 5 are connected to the optical fiber coupler 43, and the third optical fiber 16 and the fifth optical fiber 18 are connected to the optical fiber wavelength division multiplexer 44.

[0028] See Figure 4 As shown, the second structure of the wavelength division multiplexing beamsplitter 17 includes a first optical fiber 3, a second optical fiber 15, a third optical fiber 16, a fourth optical fiber 5, a fifth optical fiber 18, a seventh optical fiber collimator 46, an eighth optical fiber collimator 47, a ninth optical fiber collimator 48, a third polarization beamsplitter 49, a third waveplate 50, a fourth polarization beamsplitter 51, and a wavelength division multiplexing collimator 52. The output light of the ninth optical fiber collimator 48 sequentially passes through the third polarization beamsplitter 49, the third waveplate 50, the fourth polarization beamsplitter 51, and the wavelength division multiplexing beamsplitter. The multiplexed collimator 52 is used. The output light of the third polarization beam splitter 49 passes through the ninth fiber collimator 48 and the seventh fiber collimator 46. The output light of the fourth polarization beam splitter 51 passes through the eighth fiber collimator 47 and the wavelength division multiplexing collimator 52. The first fiber 3 is connected to the eighth fiber collimator 47. The second fiber 15 is connected to the seventh fiber collimator 46. The third fiber 16 and the fifth fiber 18 are connected to the wavelength division multiplexing collimator 52. The fourth fiber 5 is connected to the ninth fiber collimator 48.

[0029] See Figure 5 As shown, the third structure of the wavelength division multiplexing beamsplitter 17 includes a first optical fiber 3, a second optical fiber 15, a third optical fiber 16, a fourth optical fiber 5, a fifth optical fiber 18, a seventh optical fiber collimator 46, an eighth optical fiber collimator 47, a ninth optical fiber collimator 48, a third polarization beamsplitter 49, a fourth polarization beamsplitter 51, and a wavelength division multiplexing collimator 52; the output light of the ninth optical fiber collimator 48 passes sequentially through the third polarization beamsplitter 49, the fourth polarization beamsplitter 51, and the wavelength division multiplexing collimator 52. The output light from the third polarization beam splitter 49 passes through the ninth fiber collimator 48 and the seventh fiber collimator 46; the output light from the fourth polarization beam splitter 51 passes through the eighth fiber collimator 47 and the wavelength division multiplexing collimator 52. The first fiber 3 is connected to the eighth fiber collimator 47, the second fiber 15 is connected to the seventh fiber collimator 46, the third fiber 16 and the fifth fiber 18 are connected to the wavelength division multiplexing collimator 52, and the fourth fiber 5 is connected to the ninth fiber collimator 48.

[0030] In this embodiment, the function of the wavelength division multiplexing beam splitter 17 is as follows: when light is input into the fifth fiber 18, light is output from the fourth fiber 5 and the second fiber 15; when light is input into the second fiber 15, light is output from the first fiber 3 and the fifth fiber 18; when pump light is input into the third fiber 16, it is reflected by the wavelength division multiplexing beam splitter 17 into the fifth fiber 18.

[0031] In this embodiment, the first online coupling method of the system is as follows: fusion splice and connect all optical fibers in the system; turn on the second light source 30, adjust the angle and displacement of the first optical fiber collimator 6 to maximize the reading of the second power meter 36, and fix the first optical fiber collimator 6; turn off the second light source 30, turn on the first light source 29, adjust the angle and displacement of the second optical fiber collimator 21 to maximize the reading of the first power meter 42; turn off the first light source 29, turn on the pump light source 38, adjust the angle and displacement of the second optical fiber collimator 21 to maximize the reading of the second power meter 36, and fix the second optical fiber collimator 21.

[0032] In this embodiment, the second online coupling method of the system is as follows: turn on the second light source 30, adjust the angle and displacement of the first fiber collimator 6 to maximize the reading of the second power meter 36, and fix the first fiber collimator 6; adjust the angle and displacement of the third fiber collimator 9 to maximize the output optical power of the seventh fiber 8 and fix it; turn on the first light source 29, adjust the angle and displacement of the second fiber collimator 21 to maximize the overlap of the two light spots output by the first polarization beam splitter 7 or maximize the output optical power of the seventh fiber 8, and fix the second fiber collimator 21.

[0033] In this embodiment, the third online coupling method of the system is as follows: adjust the angle and displacement of the fourth fiber collimator 25 and the fifth fiber collimator 11 to maximize and fix the coupling efficiency of the fourth fiber collimator 25 and the fifth fiber collimator 11; turn on the second light source 30, adjust the angle and displacement of the first fiber collimator 6 to maximize the output optical power of the ninth fiber 24, and fix the first fiber collimator 6; turn off the second light source 30, turn on the first light source 29, adjust the angle and displacement of the second fiber collimator 21 to maximize the output optical power of the eighth fiber 10, and fix the second fiber collimator 21.

[0034] In this embodiment, the fourth online coupling method of the system is as follows: turn on the second light source 30, adjust the angle and displacement of the first fiber collimator 6 to maximize the output optical power of the tenth fiber 28, and fix the first fiber collimator 6; turn off the second light source 30, turn on the first light source 29, adjust the angle and displacement of the second fiber collimator 21 to maximize the output optical power of the tenth fiber 28, and fix the second fiber collimator 21.

[0035] The working principle of the mode-locked fiber laser system based on the online coupling method of the present invention is as follows:

[0036] The online coupling method is based on adjusting the coupling of the first fiber collimator 6 and the second fiber collimator 21 in the mode-locked fiber laser system. It is achieved by direct coupling between the two collimators, coupling of the two collimators to the same collimator, and overlapping of the output light spots of the two collimators. At the same time, it is also necessary to ensure that the back-and-forth optical paths overlap to meet the interference conditions of the nonlinear amplifying ring mirror mode-locking technology.

[0037] The working principle of the mode-locked fiber laser is based on nonlinear amplifying ring mirror mode-locking technology. The pump source 38 couples the pump light to the wavelength division multiplexing beam splitter 17 through the thirteenth fiber 39, the third port 14, and the third fiber 16, causing the gain fiber 19 to spontaneously emit continuous light. The continuous light output from the first fiber collimator 6 and the second fiber collimator 21 passes sequentially through the first polarization beam splitter 7, the Faraday rotator 22, the first waveplate 23, the second polarization beam splitter 26, and the second waveplate 12. After being reflected by the mirror 13, it passes sequentially through the second waveplate 12 back to the second polarization beam splitter 26. After passing through the second polarization beam splitter 26, the continuous light is split into linearly polarized light. The linearly polarized light continues to pass through the first waveplate. After passing through the Faraday rotator 22 and the first waveplate 23, the light becomes elliptically polarized. This elliptically polarized light is split into two beams with different polarization directions in the first polarization beam splitter 7. These two beams enter the first fiber collimator 6 and the second fiber collimator 21, respectively, and propagate simultaneously along the slow or fast axis of the fourth fiber 5 and the sixth fiber 20. After completing one loop, the two beams are output from the first fiber collimator 6 and the second fiber collimator 21, respectively. At this point, the two beams have accumulated different nonlinear phase shifts. After passing through the first polarization beam splitter 7, the Faraday rotator 22, and the first waveplate 23, the beams with the same polarization components interfere in the second polarization beam splitter 26. This process constitutes a nonlinear amplifying ring mirror. Due to the nonlinear effect of the optical fiber, the accumulated nonlinear phase shift difference between the two beams output from the first fiber collimator 6 and the second fiber collimator 21 controls the intensity modulation, increasing the transmittance of strong light and decreasing the transmittance of weak light, thus exhibiting saturable absorption characteristics. Thus, when the spontaneously emitted laser from the pump travels back and forth in the structure designed in this embodiment, it forms a stable pulse after undergoing saturable absorption.

[0038] When the laser system is working, the first fiber 3, the second fiber 15, the seventh fiber 8, the eighth fiber 10, the ninth fiber 24, and the tenth fiber 28 can all output ultrashort pulses. Among them, the pulses output by the first fiber 3 and the second fiber 15 have the highest quality.

[0039] This invention is based on mode-locking using a nonlinear amplifying ring mirror. The online coupling method is based on the laser system itself, allowing for online adjustment of the collimator coupling without the aid of external equipment. Furthermore, the online coupling method makes fiber fusion and collimator coupling two independent steps, simplifying the manufacturing process. Fusing all fibers first is beneficial for increasing the repetition rate. This is because in traditional coupling methods, fiber fusion is limited by the collimator position, requiring the fiber fusion splicer to be placed within the loop, necessitating the reservation of a long fiber length. In contrast, the online coupling method of this invention fused all fiber components linearly, eliminating the limitations of traditional methods and allowing for shorter cavity lengths. While maintaining a high repetition rate, the wavelength division multiplexing beam splitter's pigtail can output high-quality pulses within the loop. When the collimator coupling efficiency of the laser system decreases, only the collimator needs to be adjusted to improve coupling efficiency; there is no need to disconnect the fiber components and connect to an external coupling system for recoupling, avoiding the problem of fiber component failure.

[0040] Although embodiments of the present invention have been described in conjunction with the accompanying drawings, the patent owner may make various modifications or alterations within the scope of the appended claims, as long as they do not exceed the protection scope described in the claims of the present invention, they shall be within the protection scope of the present invention.

Claims

1. A mode-locked fiber laser system based on an online coupling method, characterized in that: The application relates to an online coupling module (1), a wavelength division multiplexing beam splitter (17), a fifth optical fiber (18), a gain optical fiber (19), a sixth optical fiber (20), a fourth optical fiber (5), a first optical fiber collimator (6), a second optical fiber collimator (21), a first polarization beam splitter (7), a Faraday rotator (22), a first wave plate (23), a second polarization beam splitter (26), a second wave plate (12), a mirror (13), a third optical fiber collimator (9), a fourth optical fiber collimator (25), a fifth optical fiber collimator (11) and a sixth optical fiber collimator (27), the online coupling module (1) is connected with the wavelength division multiplexing beam splitter (17), the fifth optical fiber (18), the gain optical fiber (19) and the sixth optical fiber (20) are sequentially fused, the fifth optical fiber (18) is connected with the wavelength division multiplexing beam splitter (17), the wavelength division multiplexing beam splitter (17) is connected with the first optical fiber collimator (6) through the fourth optical fiber (5), output light of the first optical fiber collimator (6) sequentially passes through the first polarization beam splitter (7), the Faraday rotator (22), the first wave plate (23), the second polarization beam splitter (26), the second wave plate (12), the mirror (13) and the sixth optical fiber collimator (27), output light of the first polarization beam splitter (7) passes through the first optical fiber collimator (6), the second optical fiber collimator (21) and the third optical fiber collimator (9), the third optical fiber collimator (9) is connected with a seventh optical fiber (8); output light of the second polarization beam splitter (26) passes through the fourth optical fiber collimator (25) and the fifth optical fiber collimator (11), the fifth optical fiber collimator (11) is connected with an eighth optical fiber (10), the fourth optical fiber collimator (25) is connected with a ninth optical fiber (24), and the sixth optical fiber collimator (27) is connected with a tenth optical fiber (28). The online coupling module (1) includes a third port (14), a thirteenth optical fiber (39), a pump light source (38), a second port (4), a fifteenth optical fiber (35), a first optical fiber circulator (40), an eleventh optical fiber (37), a first light source (29), a fourteenth optical fiber (41), a first power meter (42), a first port (2), a seventeenth optical fiber (33), a second optical fiber circulator (32), a twelfth optical fiber (31), a second light source (30), a sixteenth optical fiber (34) and a second power meter (36), the first port (2), the second port (4) and the third port (14) are connected with a wavelength division multiplexing beam splitter (17); the third port (14), the thirteenth optical fiber (39) and the pump light source (38) are sequentially connected; the second port (4), the fifteenth optical fiber (35), the first optical fiber circulator (40), the eleventh optical fiber (37) and the first light source (29) are sequentially connected; the first optical fiber circulator (40) is connected with the first power meter (42) through the fourteenth optical fiber (41); the first port (2), the seventeenth optical fiber (33), the second optical fiber circulator (32), the twelfth optical fiber (31) and the second light source (30) are sequentially connected; the second optical fiber circulator (32) is connected with the second power meter (36) through the sixteenth optical fiber (34).

2. The online coupling method based mode-locked fiber laser system according to claim 1, wherein, The wavelength division multiplexing beam splitter (17) includes a first optical fiber (3), a second optical fiber (15), a third optical fiber (16), a fourth optical fiber (5), a fifth optical fiber (18), a fiber coupler (43) and a fiber wavelength division multiplexer (44), the fiber coupler (43) is connected with the fiber wavelength division multiplexer (44) through an eighteenth optical fiber (45), the first optical fiber (3), the second optical fiber (15) and the fourth optical fiber (5) are connected with the fiber coupler (43), the third optical fiber (16) and the fifth optical fiber (18) are connected with the fiber wavelength division multiplexer (44); when the fifth optical fiber (18) inputs light, the fourth optical fiber (5) and the second optical fiber (15) output light; when the second optical fiber (15) inputs light, the first optical fiber (3) and the fifth optical fiber (18) output light; when the third optical fiber (16) inputs pump light, it is reflected into the fifth optical fiber (18) through the wavelength division multiplexing beam splitter (17).

3. The online coupling method based mode-locked fiber laser system according to claim 1, wherein, The wavelength division multiplexing beam splitter (17) comprises a first optical fiber (3), a second optical fiber (15), a third optical fiber (16), a fourth optical fiber (5), a fifth optical fiber (18), a seventh optical fiber collimator (46), an eighth optical fiber collimator (47), a ninth optical fiber collimator (48), a third polarization beam splitter (49), a third wave plate (50), a fourth polarization beam splitter (51) and a wavelength division multiplexing collimator (52), the ninth optical fiber collimator (48) outputs light in turn through the third polarization beam splitter (49), the third wave plate (50), the fourth polarization beam splitter (51) and the wavelength division multiplexing collimator (52), the third polarization beam splitter (49) outputs light through the ninth optical fiber collimator (48) and the seventh optical fiber collimator (46), the fourth polarization beam splitter (51) outputs light through the eighth optical fiber collimator (47) and the wavelength division multiplexing collimator (52), the first optical fiber (3) is connected with the eighth optical fiber collimator (47), the second optical fiber (15) is connected with the seventh optical fiber collimator (46), the third optical fiber (16) and the fifth optical fiber (18) are connected with the wavelength division multiplexing collimator (52), and the fourth optical fiber (5) is connected with the ninth optical fiber collimator (48); when the fifth optical fiber (18) inputs light, the fourth optical fiber (5) and the second optical fiber (15) output light; when the second optical fiber (15) inputs light, the first optical fiber (3) and the fifth optical fiber (18) output light; when the third optical fiber (16) inputs pump light, the pump light is reflected into the fifth optical fiber (18) through the wavelength division multiplexing beam splitter (17).

4. The online coupling method based mode-locked fiber laser system of claim 1, wherein, The wavelength division multiplexing beam splitter (17) comprises a first optical fiber (3), a second optical fiber (15), a third optical fiber (16), a fourth optical fiber (5), a fifth optical fiber (18), a seventh optical fiber collimator (46), an eighth optical fiber collimator (47), a ninth optical fiber collimator (48), a third polarization beam splitter (49), a fourth polarization beam splitter (51) and a wavelength division multiplexing collimator (52); the ninth optical fiber collimator (48) outputs light in turn through the third polarization beam splitter (49), the fourth polarization beam splitter (51) and the wavelength division multiplexing collimator (52); the third polarization beam splitter (49) outputs light through the ninth optical fiber collimator (48) and the seventh optical fiber collimator (46); the fourth polarization beam splitter (51) outputs light through the eighth optical fiber collimator (47) and the wavelength division multiplexing collimator (52), the first optical fiber (3) is connected with the eighth optical fiber collimator (47), the second optical fiber (15) is connected with the seventh optical fiber collimator (46), the third optical fiber (16) and the fifth optical fiber (18) are connected with the wavelength division multiplexing collimator (52), and the fourth optical fiber (5) is connected with the ninth optical fiber collimator (48); when the fifth optical fiber (18) inputs light, the fourth optical fiber (5) and the second optical fiber (15) output light; when the second optical fiber (15) inputs light, the first optical fiber (3) and the fifth optical fiber (18) output light; when the third optical fiber (16) inputs pump light, the pump light is reflected into the fifth optical fiber (18) through the wavelength division multiplexing beam splitter (17).

5. The online coupling method based mode-locked fiber laser system according to claim 1, wherein, The on-line coupling method of the system is: opening the second light source (30), adjusting the angle and displacement of the first optical fiber collimator (6), making the second power meter (36) show the maximum value, fixing the first optical fiber collimator (6); closing the second light source (30), opening the first light source (29), adjusting the angle and displacement of the second optical fiber collimator (21), making the first power meter (42) show the maximum value; closing the first light source (29), opening the pump light source (38), adjusting the angle and displacement of the second optical fiber collimator (21), making the second power meter (36) show the maximum value, fixing the second optical fiber collimator (21).

6. The online coupling method based mode-locked fiber laser system according to claim 1, wherein, The on-line coupling method of the system is: opening the second light source (30), adjusting the angle and displacement of the first optical fiber collimator (6), making the second power meter (36) show the maximum value, fixing the first optical fiber collimator (6); adjusting the angle and displacement of the third optical fiber collimator (9), making the seventh optical fiber (8) output the maximum optical power and fixing; opening the first light source (29), adjusting the angle and displacement of the second optical fiber collimator (21), making the two light spots output by the first polarization beam splitter (7) have the maximum coincidence degree or the seventh optical fiber (8) output the maximum optical power, fixing the second optical fiber collimator (21).

7. The online coupling method based mode-locked fiber laser system according to claim 1, wherein, The on-line coupling method of the system is: adjusting the angle and displacement of the fourth optical fiber collimator (25) and the fifth optical fiber collimator (11), making the coupling efficiency of the fourth optical fiber collimator (25) and the fifth optical fiber collimator (11) maximum and fixing; opening the second light source (30), adjusting the angle and displacement of the first optical fiber collimator (6), making the ninth optical fiber (24) output the maximum optical power, fixing the first optical fiber collimator (6); closing the second light source (30), opening the first light source (29), adjusting the angle and displacement of the second optical fiber collimator (21), making the eighth optical fiber (10) output the maximum optical power, fixing the second optical fiber collimator (21).

8. The online coupling method based mode-locked fiber laser system of claim 1, wherein, The on-line coupling method of the system is: opening the second light source (30), adjusting the angle and displacement of the first optical fiber collimator (6), making the tenth optical fiber (28) output the maximum optical power, fixing the first optical fiber collimator (6); closing the second light source (30), opening the first light source (29), adjusting the angle and displacement of the second optical fiber collimator (21), making the tenth optical fiber (28) output the maximum optical power, fixing the second optical fiber collimator (21).

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