Bi-pass pre-chirp amplification system

Abstract

The utility model belongs to the technical field of laser, and discloses a bi-pass pre-chirp amplification system, which sequentially comprises a seed source, a signal source, a signal source, a signal source and a signal source along a light path direction, the circulator receives the signal light and outputs the signal light to the single-mode gain optical fiber; the single-mode gain fiber performs primary modulation on the signal light and then outputs the signal light to the long-period fiber grating; the long-period fiber grating performs primary mode conversion on the signal light subjected to primary modulation and then outputs the signal light to the large-mode-field double-cladding gain fiber; the pumping source generates pumping light; the laser beam combiner couples the pump light into the large-mode-field double-cladding gain optical fiber; the large-mode-field double-cladding gain fiber amplifies the signal light after the primary mode conversion and outputs the amplified signal light to the pre-chirp grating group; and the pre-chirp grating group performs pre-chirp management on the amplified laser and then reflects the laser back to the original path, and the laser is output from the circulator after secondary amplification. The gain of the amplifier is improved through bi-pass amplification, gain narrowing is inhibited, and the complexity of an amplification system is reduced.

Description

TECHNICAL FIELD

[0001] The utility model belongs to laser technology field, concretely relates to a double -pass pre -chirp amplification system. BACKGROUND

[0002] Fiber lasers have been widely used in many fields such as industrial processing, scientific research, medical treatment and the like due to its high beam quality, high efficiency, compact structure, good heat dissipation performance and the like. With the continuous growth of application demand, higher requirements are put forward to the performance indexes such as output power and pulse quality of fiber lasers. For example, in the field of industrial cutting and welding, higher power fiber lasers can improve processing speed and processing quality and reduce production cost, and in the field of scientific research, high-quality ultra-short pulse fiber lasers have important significance for precise spectral analysis and ultrafast physical process research.

[0003] In the conventional fiber laser amplification system, the mode field area of the core mode is relatively small. When the input power is high, nonlinear effects such as stimulated Brillouin scattering and stimulated Raman scattering are easily induced, which not only consumes pump energy and reduces laser output power, but also seriously affects the performance and quality of the laser. At the same time, in the process of pursuing high power output, the existing amplification technology narrows the gain in the amplification process, which causes the narrowing of the laser spectrum, and it is difficult to ensure good pulse quality and high amplification gain at the same time.

[0004] Therefore, there is an urgent need in the art for a double-pass pre-chirp amplification system to solve the above technical problems. SUMMARY

[0005] Therefore, the purpose of the utility model is to solve the above problems and provide a double-pass pre-chirp amplification system.

[0006] To solve the above technical problems, the utility model provides a double-pass pre-chirp amplification system, which comprises in sequence along the optical path direction:

[0007] A seed source for emitting signal light with linear chirp;

[0008] A circulator for receiving the signal light and outputting the signal light to a single-mode gain fiber;

[0009] A single-mode gain fiber for modulating the signal light once and outputting the once-modulated signal light to a long-period fiber grating;

[0010] A long-period fiber grating for converting the once-modulated signal light into a mode once and outputting the once-mode-converted signal light to a large-mode-area double-cladding gain fiber;

[0011] A pump source for generating pump light;

[0012] A laser combiner for coupling the pump light into a large-mode-area double-clad gain fiber;

[0013] A large-mode-area double-clad gain fiber for amplifying the signal light after the first mode conversion and outputting the amplified laser to a pre-chirped grating set;

[0014] A pre-chirped grating set for pre-chirp management of the amplified laser and reflecting the amplified laser back to the original path, and outputting the laser from the circulator after the second amplification.

[0015] As a further improvement of the utility model, the pre-chirped grating set includes a first diffraction grating, a second diffraction grating and a plane mirror.

[0016] The first diffraction grating and the second diffraction grating are arranged in parallel.

[0017] The plane mirror is placed perpendicular to the laser transmission direction.

[0018] As a further improvement of the utility model, the double-pass pre-chirped amplification system further includes an isolator, and the circulator includes a first end, a second end and a third end.

[0019] The first end of the circulator is connected with the seed source through the isolator, and the isolator is used for isolating the pump light and the amplified laser, and preventing the pump light and the second amplified laser from returning to the seed source.

[0020] The second end of the circulator is connected with the single-mode gain fiber.

[0021] The third end of the circulator is used for outputting the second amplified laser.

[0022] As a further improvement of the utility model, the double-pass pre-chirped amplification system further includes a half-wave plate, which is located between the large-mode-area double-clad gain fiber and the pre-chirped grating set along the optical path direction, and is used for adjusting the polarization state of the laser.

[0023] As a further improvement of the utility model, the single-mode gain fiber performs first modulation on the signal light, specifically, the single-mode gain fiber converts the signal light from a multimode to a core fundamental mode.

[0024] As a further improvement of the utility model, the long-period fiber grating performs first mode conversion on the first modulated signal light, specifically, the long-period fiber grating converts the signal light from a core fundamental mode to a cladding mode.

[0025] As a further improvement of the utility model, the laser is twice amplified, specifically comprising:

[0026] The large-mode-area double-cladding gain fiber performs secondary amplification on the amplified laser.

[0027] The long-period fiber grating performs secondary mode conversion on the twice-amplified laser.

[0028] The single-mode gain fiber performs secondary modulation on the twice-mode-converted laser.

[0029] As a further improvement of the utility model, the long-period fiber grating performs secondary mode conversion on the twice-amplified laser, specifically: the long-period fiber grating converts the twice-amplified laser from cladding mode to core fundamental mode.

[0030] As a further improvement of the utility model, the single-mode gain fiber performs secondary modulation on the twice-mode-converted laser, specifically: the single-mode gain fiber performs self-phase modulation on the twice-amplified laser to expand the spectrum of the twice-amplified laser of the core fundamental mode.

[0031] As a further improvement of the utility model, the second diffraction grating is installed on an adjustable displacement platform.

[0032] Compared with the prior art, the double-pass pre-chirp amplification system provided by the utility model increases the mode field area through mode conversion of the long-period fiber grating, effectively reduces the nonlinear effect under high power, improves the stability and laser quality of the system, uses double-pass amplification technology, i.e. the laser passes through the large-mode-area double-cladding gain fiber twice, significantly improves the power and intensity of the output laser, has higher gain than the single-pass amplification system, improves the overall efficiency of the system, optimizes the characteristics of the laser pulse through pre-chirp management of the pre-chirp grating group, compresses the picosecond seed pulse with chirp to femtosecond, prepares for the subsequent amplification process of the pulse peak power, excitation of self-phase modulation, etc., and finally realizes high-quality laser pulse output. The double-pass amplification technology not only improves the power, but also effectively suppresses the noise in the system, improves the signal-to-noise ratio of the signal, makes the laser signal more prominent, and further improves the performance of the system. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical scheme in the embodiments of the utility model or the prior art, the drawings needed to be used in the embodiment or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only a part of the embodiments of the utility model, not all the embodiments. For those skilled in the art, other drawings obtained according to these drawings without creative labor belong to the protection scope of the application.

[0034] Figure 1 is a structure schematic view of a double-pass pre-chirp amplification system provided by the embodiment of the utility model.

[0035] The figure mark explanation: 1 is seed source, 2 is circulator, 21 is the first end of circulator, 22 is the second end of circulator 23 is the third end of circulator, 3 is single-mode gain optical fiber, 4 is long-period fiber grating, 5 is pump source, 6 is laser beam combiner, 7 is large-mode-area double-cladding gain optical fiber, 8 is pre-chirp grating group, 81 is first diffraction grating, 82 is second diffraction grating, 83 is plane mirror, 9 is isolator, 10 is half-wave plate. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical scheme and advantages of the utility model more clear and obvious, the utility model is further described in detail below by combining with the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the utility model, and are not used to limit the utility model.

[0037] In order to make the description of the disclosure more detailed and complete, the following describes the embodiments of the utility model and specific examples; But this is not the only form of implementation or use of the specific embodiments of the utility model. The embodiments include the features of multiple specific embodiments and the method steps and order used to construct and operate these specific embodiments. However, other specific embodiments can also be used to achieve the same or equivalent functions and step sequences. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the present application.

[0038] It should be noted that the terms "first", "second" and the like in the specification and claims of the utility model and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the utility model described herein can be implemented in an order other than those illustrated or described herein.

[0039] In the description of the embodiments of the utility model, unless otherwise specified, " / " represents the meaning of or, for example, A / B can represent A or B, the "and / or" in the text is only a kind of description of the association relationship of associated object, it can exist three kinds of relations, for example, A and / or B, can represent: exist A alone, exist A and B simultaneously, exist B alone these three cases, in addition, in the description of the embodiments of the present application, "multiple" refers to two or more than two, other quantifiers should be understood similar thereto, the preferred embodiments described herein are only used to illustrate and explain the utility model, and are not used to limit the utility model, and in the case of no conflict, the embodiments of the present application and the features in the embodiments can be combined with each other.

[0040] Please refer to Figure 1 The utility model provides a kind of double-pass pre-chirp amplification system to solve the problem of existing amplification system, when input power is higher, it is easy to cause nonlinear effect, it is difficult to guarantee good pulse quality and higher amplification gain simultaneously.

[0041] Specifically, Figure 1 The structure diagram of the double-pass pre-chirp amplification system provided by the utility model embodiment, the double-pass pre-chirp amplification system includes in turn along the direction of optical path: seed source 1, circulator 2, single-mode gain optical fiber 3, long-period fiber grating 4, laser beam combiner 6, large-mode-area double-cladding gain fiber 7 and pre-chirp grating group 8, laser is amplified twice in large-mode-area double-cladding gain fiber 7, significantly improve the gain of amplifier, improve system efficiency, while effectively improve the signal-to-noise ratio of signal, reduce system noise.

[0042] Specifically, the seed source 1 used in the embodiment is picosecond seed source, the seed source 1 is used to emit signal light with linear chirp, the seed source 1 provides signal light with linear chirp to provide basis for subsequent amplification operation, the chirp characteristics can provide basis for subsequent pre-chirp management and other operations, which helps to realize accurate control and optimization of laser pulse.

[0043] Circulator 2 is used to receive the laser signal, and output the laser signal to single-mode gain optical fiber 3, to ensure that the laser signal can be transmitted according to the predetermined optical path direction. The one-way transmission characteristics of circulator 2 can avoid the reverse transmission of signal, and ensure the stability of the system and the accuracy of signal transmission.

[0044] Single-mode gain optical fiber 3 is used to modulate the signal light once, and output the modulated signal light to long-period fiber grating 4. Through single-mode gain optical fiber 3, the signal light can be preliminarily processed and optimized to some extent, providing a better signal basis for subsequent amplification and mode conversion operations. The modulated signal light is output to long-period fiber grating 4 to prepare for subsequent mode conversion.

[0045] The long-period fiber grating 4 is used for mode conversion of the once modulated signal light, and outputs the once mode-converted signal light to the large-mode-area double-cladding gain fiber 7. By converting the mode of the laser light, such as converting the core fundamental mode to the cladding mode, the mode field area can be effectively increased, thereby reducing the influence of nonlinear effects and avoiding fiber damage. At the same time, the mode-converted signal light is output to the large-mode-area double-cladding gain fiber 7, which creates favorable conditions for subsequent amplification.

[0046] The pump source 5 is used to generate pump light, which provides an energy source for subsequent amplification. The pump light is crucial for the population inversion in the large-mode-area double-cladding gain fiber 7, and the pump source 5 provides key energy supply for laser amplification.

[0047] The laser combiner 6 is used to couple the pump light into the large-mode-area double-cladding gain fiber 7. By coupling the pump light into the large-mode-area double-cladding gain fiber 7 through the laser combiner 6, it can ensure that the pump light effectively enters the gain fiber, realizes population inversion, and thus provides energy support for laser amplification.

[0048] The large-mode-area double-cladding gain fiber 7 is used to amplify the once mode-converted signal light and output the amplified signal light to the pre-chirped grating group 8. The large-mode-area double-cladding gain fiber 7 amplifies the once mode-converted signal light, which improves the power of the laser. The large-mode-area double-cladding gain fiber 7 has a large mode field area, which can withstand higher power and reduce nonlinear effects. The amplified laser light is output to the pre-chirped grating group 8, which prepares for further pre-chirp management and secondary amplification.

[0049] The pre-chirped grating group 8 is used for pre-chirp management of the amplified laser light and reflects the amplified laser light back to the original path. The laser light is output from the circulator 2 after secondary amplification. The pre-chirped grating group 8 manages the chirp characteristics of the laser pulse by adjusting the chirp characteristics of the laser pulse, which provides more favorable conditions for subsequent amplification. At the same time, the amplified laser light is reflected back to the original path, so that the laser light can be amplified twice and then output from the circulator 2 after processing, which helps to improve the quality and output power of the laser pulse.

[0050] The double-pass pre-chirped amplification system provided by the embodiment increases the mode field area through mode conversion of the long-period fiber grating 4, effectively reduces the nonlinear effect under high power, improves the stability and laser quality of the system, uses double-pass amplification technology, that is, the laser passes through the large-mode-field double-cladding gain fiber 7 twice, significantly improves the power and intensity of the output laser, has higher gain than the single-pass amplification system, improves the overall efficiency of the system, and the pre-chirped grating group 8 is used for pre-chirped management to optimize the characteristics of the laser pulse, compresses the picosecond seed pulse with chirp to femtosecond, prepares for improving the pulse peak power in the subsequent amplification process and exciting self-phase modulation, and finally realizes high-quality laser pulse output.

[0051] The double-pass pre-chirped amplification system can be widely applied to fields requiring high-power and high-quality laser pulses, such as laser processing (cutting, welding, drilling, etc.), laser medical treatment (ophthalmic surgery, skin treatment, etc.), optical communication (high-speed signal transmission, etc.), scientific research (optics, research on ultrafast physical processes, etc.), and the like, and provides strong technical support for the development and progress of these fields.

[0052] As a further improvement of the utility model, the pre-chirped grating group 8 includes a first diffraction grating 81, a second diffraction grating 82 and a plane mirror 83; the first diffraction grating 81 and the second diffraction grating 82 are arranged in parallel, and the first diffraction grating 81 and the second diffraction grating 82 cooperate to process the laser amplified by the large-mode-field double-cladding gain fiber 7, the first diffraction grating 81 and the second diffraction grating 82 form a grating pair, the distance between the grating pair is adjusted to change the chirp amount of the incident laser pulse, the chirp amount of the laser pulse is accurately adjusted, the laser pulse is accurately compressed from picosecond to femtosecond, the pre-chirped management of the laser pulse is realized, and the efficiency and quality of laser amplification are improved.

[0053] Further, the plane mirror 83 is placed perpendicular to the laser transmission direction. The plane mirror 83 is placed perpendicular to the laser transmission direction, which ensures that the laser can be accurately reflected back to the large-mode-area double-cladding gain fiber 7, so that the double-pass amplification process is more stable and efficient. In the pre-chirp management process, the plane mirror 83 reflects the laser processed by the first diffraction grating 81 and the second diffraction grating 82 back to the original path, so that the laser can enter the large-mode-area double-cladding gain fiber 7 again. When the laser is reflected back to the double-cladding gain fiber, the laser can obtain energy again, realizing secondary amplification. By reflecting the laser back to the original light path, the laser can pass through the previous optical elements and gain fiber again, thereby further adjusting and optimizing its characteristics, ultimately realizing higher quality and higher power laser output. At the same time, the laser processed by the pre-chirp grating group 8 can better suppress nonlinear effects and noise during secondary amplification, because its pulse characteristics have been optimized, which is more conducive to efficient energy absorption and amplification, thereby significantly improving the power and intensity of the output secondary amplified laser. The pre-chirp grating group 8 composed of the grating pair and the plane mirror 83 compresses the picosecond seed source with chirp to femtosecond pulses, significantly compresses the pulse width, and obtains a large amount of nonlinear phase shift, and the gain spectrum bandwidth is greatly increased, exceeding the gain bandwidth of the double-pass pre-chirp amplification system itself.

[0054] As a further improvement of the utility model, the double-pass pre-chirp amplification system further comprises an isolator 9, and the circulator 2 comprises a first end 21, a second end 22 and a third end 23. The first end 21 of the circulator 2 is connected with the seed source 1 through the isolator 9, and the isolator 9 is used to isolate the pump light and the amplified laser, to prevent the pump light and the secondary amplified laser from returning to the seed source 1. The first end 21 of the circulator is connected with the seed source 1 through the isolator 9, and the characteristics of the isolator 9 are used to effectively isolate the pump light and the secondary amplified laser, to prevent the pump light and the secondary amplified laser from returning to the seed source 1. This avoids the pump light and the high-energy secondary amplified laser from flowing back to the seed source 1, which would damage the seed source 1 and affect the performance and service life of the seed source 1. This effectively avoids system failure, prolongs the service life of the seed source 1, and ensures stable operation of the entire system.

[0055] Further, the second end 22 of the circulator 2 is connected with the single-mode gain fiber 3. The second end 22 of the circulator is connected with the single-mode gain fiber 3, so that the signal light received from the circulator 2 can be smoothly transmitted to the single-mode gain fiber 3, to modulate the signal light once. This ensures the orderly flow of laser in the system, and prepares for the mode conversion of the long-period fiber grating 4 and the amplification process of the large-mode-area double-cladding gain fiber 7.

[0056] Specifically, the third end 23 of the circulator 2 is used for outputting the twice-amplified laser, and the third end 23 of the circulator is used as an output end of the system, for outputting the twice-amplified laser, after a series of processing, including modulation of the single-mode gain optical fiber 3, mode conversion of the long-period fiber grating 4, double-pass amplification of the large-mode-area double-cladding gain optical fiber 7 and pre-chirp management of the pre-chirp grating group 8, the twice-amplified laser is finally output from the third end 23 of the circulator 2, and high-quality laser signals are provided for subsequent applications.

[0057] As a further improvement of the utility model, the double-pass pre-chirp amplification system further comprises a half-wave plate, the half-wave plate is located between the large-mode-area double-cladding gain optical fiber 7 and the pre-chirp grating group 8 along the light path direction, and is used for adjusting the polarization state of the laser. By arranging the half-wave plate 10 between the large-mode-area double-cladding gain optical fiber 7 and the pre-chirp grating group 8, the half-wave plate 10 adjusts the polarization of the laser, and by optimizing the polarization state, the amplification process of the laser in the gain optical fiber can be optimized, so that the amplification efficiency of the laser is improved. At the same time, for the subsequent pre-chirp grating group 8, the appropriate polarization state can improve the diffraction efficiency of the grating, so that the laser pulse is more effectively pre-chirped, the pulse compression of the laser is ensured, and the quality of the finally output laser is ensured, and the performance and efficiency of the whole system are improved.

[0058] As a further improvement of the utility model, the single-mode gain optical fiber 3 modulates the signal light once, specifically: the single-mode gain optical fiber 3 converts the signal light from multimode to core base mode. The single-mode gain optical fiber 3 modulates the signal light once, specifically, the laser signal is converted from multimode to core base mode. When the multimode signal light propagates in the optical fiber, mode dispersion will be generated due to different propagation speeds and paths, which may cause problems such as pulse broadening and signal distortion, affecting the quality of the signal light and the subsequent processing process. When the single-mode gain optical fiber 3 converts the signal light into core base mode, only one mode is allowed to propagate in the optical fiber, avoiding the mode dispersion problem caused by multimode propagation, and significantly improving the quality of the laser signal. Since the mode dispersion caused by multimode transmission is eliminated, the laser signal can maintain a narrower pulse width and more stable time characteristics in the subsequent transmission and processing process, which helps to improve the overall performance of the system.

[0059] As a further improvement of the utility model, long period fiber grating 4 carries out once mode conversion to the signal light after once modulation, specifically: long period fiber grating 4 converts the signal light from fiber core base mode to cladding mode. Long period fiber grating 4 converts the signal light after once modulation by single mode gain optical fiber 3 from fiber core base mode to cladding mode, and its main purpose is to increase mode field area. The mode field area of fiber core base mode is relatively small, and when the input power is high, nonlinear effects such as stimulated Brillouin scattering and stimulated Raman scattering are easily caused, which can reduce the output power of signal light, cause spectral broadening and pulse distortion, and limit the performance improvement of the system. Converting the signal light into cladding mode can effectively increase the mode field area and reduce the optical power density, thereby inhibiting the occurrence of nonlinear effects. In high-power fiber laser systems, small mode field area can concentrate optical field energy and easily reach the threshold of nonlinear effects. Cladding mode has a larger mode field area, and optical energy is more dispersed in the cladding, which reduces the optical field intensity and avoids or reduces the impact of nonlinear effects on the system. By converting the signal light from fiber core base mode to cladding mode through long period fiber grating 4, the nonlinear effects that may occur in the system are significantly reduced, the stability and reliability of the system are improved, energy loss and laser quality degradation caused by nonlinear effects are avoided, the occurrence of nonlinear effects is reduced, the power bearing capacity of the system is improved, and the signal light converted into cladding mode enters large mode field double-cladding gain fiber 7. Large mode field gain fiber can amplify the optical field in the cladding. Since the mode field area of the cladding mode is large, large mode field double-cladding gain fiber 7 can more effectively realize population inversion and optical signal amplification, laying a foundation for realizing higher amplification gain and better laser output.

[0060] As a further improvement of the utility model, the laser is amplified twice, specifically including: large mode field double-cladding gain fiber 7 carries out twice amplification to the amplified laser; long period fiber grating 4 carries out twice mode conversion to the twice amplified laser; long period fiber grating 4 carries out twice mode conversion to the twice amplified laser; single mode gain optical fiber 3 carries out twice modulation to the twice mode converted laser.

[0061] Specifically, the large-mode-area double-clad gain fiber 7 plays an important role in the secondary amplification of the amplified laser. During the secondary amplification, it receives the laser reflected back after being processed by the pre-chirped grating group 8 and amplifies it again. Due to the large mode area and special double-clad structure of the large-mode-area double-clad gain fiber 7, it can more effectively utilize the energy provided by the pump light to provide sufficient gain for the laser after two times of amplification. This secondary amplification significantly improves the power of the laser. After the first amplification, the power of the laser is improved to a certain extent, but it may still not meet the output power requirements of the system. The large-mode-area double-clad gain fiber 7, through the action of the gain medium inside and the pump light, performs secondary amplification on the laser, further enhancing the energy of the laser, providing a stronger energy basis for subsequent processing and final output.

[0062] Further, the long-period fiber grating 4 performs secondary mode conversion on the secondary amplified laser. The mode of the laser after secondary amplification by the large-mode-area double-clad gain fiber 7 is still in the cladding mode state. The secondary mode conversion of the long-period fiber grating 4 helps to further optimize the mode field characteristics of the laser. It can adjust the mode of the laser according to the needs of the system to adapt to the subsequent processing steps. Adjusting the secondary amplified laser to a mode that is more conducive to processing by the single-mode gain fiber 3 prepares for subsequent secondary modulation, while also further suppressing nonlinear effects to ensure the stability and performance of the system.

[0063] Specifically, the single-mode gain fiber 3 performs secondary modulation on the secondary mode-converted laser. The single-mode gain fiber 3 performs secondary modulation on the laser after secondary mode conversion, which can further improve the quality of the laser signal and provide a higher quality signal for the final output. Further optimize the time characteristics of the laser to make it more suitable for high-power output and high-beam-quality requirements, and adjust the spectral characteristics of the laser to meet specific application requirements.

[0064] The combination of secondary amplification, secondary mode conversion, and secondary modulation improves the overall output power of the system. Through the secondary amplification of the large-mode-area double-clad gain fiber 7, the output power of the system is significantly improved, meeting the requirements of high-power laser output. At the same time, the secondary mode conversion of the long-period fiber grating 4 and the secondary modulation of the single-mode gain fiber 3 ensure that while the power is improved, the quality and performance of the laser are also optimized. By suppressing nonlinear effects, optimizing mode field characteristics, and adjusting signal characteristics, the final output laser can have better beam quality, narrower pulse width, and higher energy stability.

[0065] As a further improvement of the utility model, the long period fiber grating 4 carries out secondary mode conversion to the twice amplified laser, specifically: the long period fiber grating 4 converts the twice amplified laser from cladding mode to core fundamental mode. The long period fiber grating 4 converts the twice amplified laser into core fundamental mode, which can provide more stable and more suitable mode for subsequent processing and final output. The core fundamental mode has a relatively single propagation mode in the optical fiber, avoiding the mode instability and complex mode coupling effect that may exist in the cladding mode, thereby facilitating the acquisition of high-quality output beam. The conversion into core fundamental mode prepares for single-mode output, ensuring that the system can finally realize high-quality single-mode output through the components such as the circulator 2. At the same time, the secondary mode conversion of the long period fiber grating 4 undertakes the secondary amplification operation of the large-mode-area double-cladding gain fiber 7, converts the cladding mode laser after secondary amplification into core fundamental mode, and provides an ideal input for the subsequent secondary modulation of the single-mode gain fiber 3. The coherence and efficiency of the system from secondary amplification to final output are ensured. The single-mode gain fiber 3 can further modulate the signal based on the converted core fundamental mode, optimize the time, space and spectral characteristics of the signal, and make the final output laser meet the performance requirements of various application scenarios.

[0066] As a further improvement of the utility model, the single-mode gain fiber 3 carries out secondary modulation to the twice mode-converted laser, specifically: the single-mode gain fiber 3 increases the peak power of the twice amplified laser to realize self-phase modulation, so as to broaden the spectrum of the twice amplified laser of the core fundamental mode. The single-mode gain fiber 3 carries out secondary modulation to the laser after secondary mode conversion, specifically self-phase modulation. During the secondary amplification process, due to factors such as the saturation effect of the gain medium, gain narrowing phenomenon will be introduced. The spectrum broadening realized by the self-phase modulation of the single-mode gain fiber 3 to the twice amplified laser of the core fundamental mode can compensate for this gain narrowing. After the compensation of the self-phase modulation of the single-mode gain fiber 3, the system can maintain a relatively wide spectrum, ensuring that the laser still has good performance such as shorter pulse width, higher peak power and better time and space resolution when high-power output.

[0067] As a further improvement of the utility model, the second diffraction grating 82 is installed on the adjustable displacement platform. By installing the second diffraction grating 82 on the adjustable displacement platform, the flexibility and adjustability of the system are improved. In the pre-chirp management process, the grating pair composed of the first diffraction grating 81 and the second diffraction grating 82 plays a key control role on the chirp characteristics of the laser pulse. By changing the position of the second diffraction grating 82 on the adjustable displacement platform, the relative distance between the second diffraction grating 82 and the first diffraction grating 81 can be adjusted, thereby affecting the diffraction and interference effect of the laser pulse, and the chirp amount of the laser pulse is accurately controlled. This is crucial for compressing the picosecond seed pulse with chirp to femtosecond. Different intervals will result in different chirp compensation effects, so that the laser pulse can be compressed to the required ultrashort pulse width according to the needs, which provides conditions for the system to output high-quality ultrashort pulse laser, and helps to realize the overall optimization of the system from high-power amplification to high-quality pulse output.

[0068] The technical features of the above embodiments can be combined in any manner. To make the description concise, all possible combinations of the technical features in the above embodiments are not described, but as long as the combinations of the technical features do not exist contradictory, they should be considered as the scope of the present disclosure.

[0069] The above embodiments only express the preferred implementation of the utility model, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the utility model, a number of modifications and improvements can be made, which are within the scope of protection of the utility model. Therefore, the scope of protection of the utility model should be subject to the appended claims.

Claims

1. A dual-pass pre-chirp amplification system, characterized by, The double-pass pre-chirped amplification system comprises a seed source, a circulator, a single-mode gain fiber, a long-period fiber grating, a pump source, a laser beam combiner, a large-mode-area double-cladding gain fiber, and a pre-chirped grating set. The seed source is used for emitting signal light with linear chirp. The circulator is used for receiving the signal light and outputting the signal light to the single-mode gain fiber. The single-mode gain fiber is used for modulating the signal light once and outputting the once-modulated signal light to the long-period fiber grating. The long-period fiber grating is used for performing mode conversion on the once-modulated signal light and outputting the once-mode-converted signal light to the large-mode-area double-cladding gain fiber. The pump source is used for generating pump light. The laser beam combiner is used for coupling the pump light into the large-mode-area double-cladding gain fiber. The large-mode-area double-cladding gain fiber is used for amplifying the once-mode-converted signal light and outputting the amplified laser light to the pre-chirped grating set. The pre-chirped grating set is used for pre-chirp managing the amplified laser light and reflecting the amplified laser light back to the original path, and the laser light is output from the circulator after being amplified twice.

2. The dual-pass pre-chirped amplification system of claim 1, wherein, The pre-chirped grating set comprises a first diffraction grating, a second diffraction grating, and a plane mirror. The first diffraction grating and the second diffraction grating are arranged in parallel. The plane mirror is arranged perpendicularly to the laser light transmission direction.

3. The dual-pass pre-chirped amplification system of claim 1, wherein, The double-pass pre-chirped amplification system further comprises an isolator, and the circulator comprises a first end, a second end, and a third end. The first end of the circulator is connected to the seed source through the isolator, and the isolator is used for isolating the pump light and the amplified laser light to prevent the pump light and the twice-amplified laser light from returning to the seed source. The second end of the circulator is connected to the single-mode gain fiber. The third end of the circulator is used for outputting the twice-amplified laser light.

4. The dual-pass pre-chirped amplification system of claim 1, wherein, The double-pass pre-chirped amplification system further comprises a half-wave plate, which is arranged between the large-mode-area double-cladding gain fiber and the pre-chirped grating set along the light path direction and is used for adjusting the polarization state of the laser light.

5. The dual-pass pre-chirped amplification system of claim 1, wherein, The single-mode gain fiber modulates the signal light once, specifically, the single-mode gain fiber converts the signal light from a multi-mode to a core fundamental mode.

6. The dual-pass pre-chirped amplification system of claim 1, wherein, The long-period fiber grating performs mode conversion on the once-modulated signal light, specifically, the long-period fiber grating converts the signal light from the core fundamental mode to a cladding mode.

7. The dual-pass pre-chirped amplification system of claim 1, wherein, The laser light is amplified twice, specifically including: The large-mode-area double-cladding gain fiber amplifies the amplified laser light twice. The long-period fiber grating performs mode conversion on the twice-amplified laser light. The single-mode gain fiber modulates the twice-mode-converted laser light.

8. The dual-pass pre-chirped amplification system of claim 7, wherein, The long-period fiber grating performs mode conversion on the twice-amplified laser light, specifically, the long-period fiber grating converts the twice-amplified laser light from the cladding mode to the core fundamental mode.

9. The dual-pass pre-chirped amplification system of claim 8, wherein, The single-mode gain fiber modulates the twice-mode-converted laser light, specifically, the single-mode gain fiber self-phase modulates the twice-amplified laser light to make the spectrum of the twice-amplified laser light of the core fundamental mode broaden.

10. The dual-pass pre-chirped amplification system of claim 2, wherein, The second diffraction grating is installed on an adjustable displacement platform.

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