Bi-pass pre-chirp amplification system

Abstract

The invention 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 the light path direction, and the seed source emits signal light with linear chirp; 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 invention belongs to the field of laser technology, and in particular relates to a double-pass pre-chirp amplification system. Background Art

[0002] Fiber lasers have been widely used in many fields such as industrial processing, scientific research, and medical treatment due to their advantages of high beam quality, high efficiency, compact structure, and good heat dissipation performance. With the continuous growth of application demand, higher requirements are placed on the performance indicators of fiber lasers such as output power and pulse quality. For example, in the field of industrial cutting and welding, higher-power fiber lasers can improve processing speed and quality and reduce production costs; in the field of scientific research, high-quality ultrashort pulse fiber lasers are of great significance for precision spectral analysis and ultrafast physical process research.

[0003] In traditional fiber laser amplification systems, the mode field area of ​​the core fundamental mode is relatively small. When the input power is high, it is easy to induce nonlinear effects, such as stimulated Brillouin scattering, stimulated Raman scattering, etc. These nonlinear effects will not only consume pump energy and reduce the laser output power, but also seriously affect the performance and quality of the laser. At the same time, in the process of pursuing high-power output, the existing amplification technology, the gain narrowing problem in the amplification process will lead to the narrowing of the laser spectrum, making it difficult to simultaneously ensure good pulse quality and high amplification gain.

[0004] Based on this, the art urgently needs a dual-pass pre-chirp amplification system to solve the above technical problems. Summary of the invention

[0005] In view of this, an object of the present invention is to solve the above-mentioned problem and provide a dual-pass pre-chirp amplification system.

[0006] In order to solve the above technical problems, the present invention provides a dual-pass pre-chirp amplification system, which includes:

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

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

[0009] A single-mode gain optical fiber, used for performing a primary modulation on the signal light and outputting the primary modulated signal light to a long-period fiber grating;

[0010] A long period fiber grating, used for performing a mode conversion on the signal light after the primary modulation, and outputting the signal light after the primary mode conversion to a large mode field double-clad gain optical fiber;

[0011] A pump source, used to generate pump light;

[0012] Laser beam combiner, used to couple pump light into large mode area double-clad gain fiber;

[0013] A large mode field double-clad gain optical fiber, used for amplifying the signal light after the primary mode conversion, and outputting the amplified laser to the pre-chirped grating group;

[0014] The pre-chirp grating group is used to perform pre-chirp management on the amplified laser and reflect the amplified laser back to the original path. The laser is output from the circulator after secondary amplification.

[0015] As a further improvement of the present invention, the pre-chirp grating group includes a first diffraction grating, a second diffraction grating and a plane reflector;

[0016] The first diffraction grating is arranged in parallel with the second diffraction grating;

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

[0018] As a further improvement of the present invention, the dual-pass pre-chirp 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 to the seed source through the isolator, and the isolator 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;

[0020] The second end of the circulator is connected to the single-mode gain optical fiber;

[0021] The third end of the circulator is used to output the laser after the second amplification.

[0022] As a further improvement of the present invention, the double-pass pre-chirp amplification system also includes a half-wave plate, which is located between the large mode field double-clad gain fiber and the pre-chirp grating group along the optical path direction and is used to adjust the polarization state of the laser.

[0023] As a further improvement of the present invention, the single-mode gain optical fiber performs one modulation on the signal light, specifically: the single-mode gain optical fiber converts the signal light from multi-mode to core fundamental mode.

[0024] As a further improvement of the present invention, the long period fiber grating performs a mode conversion on the signal light after the primary modulation, specifically: the long period fiber grating converts the signal light from the core fundamental mode to the cladding mode.

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

[0026] The large mode field double-clad gain optical fiber performs secondary amplification on the amplified laser;

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

[0028] The single-mode gain optical fiber performs secondary modulation on the laser light subjected to secondary mode conversion.

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

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

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

[0032] Compared with the prior art, the present invention provides a double-pass pre-chirp amplification system, which increases the mode field area through mode conversion of long-period fiber gratings, effectively reduces the nonlinear effect under high power, improves the stability of the system and the laser quality, and utilizes double-pass amplification technology, that is, the laser passes through the large-mode-field double-clad gain fiber twice, which significantly improves the power and intensity of the output laser. Compared with the single-pass amplification system, it has a higher gain and improves the overall efficiency of the system. The pre-chirp management of the pre-chirp grating group optimizes the characteristics of the laser pulse, compresses the chirped picosecond seed pulse to femtosecond, and prepares for improving the pulse peak power of the subsequent amplification process, exciting self-phase modulation, etc., and finally achieves 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 THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only part of the embodiments of the present invention, rather than all of the embodiments. For ordinary technicians in this field, without paying creative work, other drawings obtained based on these drawings all fall within the scope of protection of this application.

[0034] Figure 1It is a structural schematic diagram of a dual-pass pre-chirp amplification system provided by an embodiment of the present invention.

[0035] Explanation of the reference numerals: 1 is a seed source, 2 is a circulator, 21 is a first end, 22 is a second end, 23 is a third end, 3 is a single-mode gain fiber, 4 is a long-period fiber grating, 5 is a pump source, 6 is a laser combiner, 7 is a large-mode-area double-clad gain fiber, 8 is a pre-chirped grating group, 81 is a first diffraction grating, 82 is a second diffraction grating, 83 is a plane reflector, 9 is an isolator, and 10 is a half-wave plate. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0037] In order to make the description of the disclosed content more detailed and complete, the following is an illustrative description of the implementation mode and specific examples of the present invention; however, this is not the only form of implementing or applying the specific embodiments of the present invention. The implementation mode covers the features of multiple specific embodiments and the method steps and their sequence for constructing and operating these specific embodiments. However, other specific embodiments can also be used to achieve the same or equal functions and step sequences. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

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

[0039] In the description of the embodiments of the present invention, unless otherwise specified, “ / ” means or, for example, A / B can mean A or B; “and / or” in the text is merely a description of the association relationship of associated objects, indicating that three relationships may exist, for example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, in the description of the embodiments of the present application, “multiple” refers to two or more than two, and other quantifiers are similar. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention, and the embodiments of the present application and the features in the embodiments may be combined with each other without conflict.

[0040] Please refer to Figure 1The present invention provides a dual-pass pre-chirp amplifier system to solve the problem in the existing amplifier system that when the input power is high, it is easy to cause nonlinear effects and it is difficult to ensure good pulse quality and high amplification gain at the same time.

[0041] Specifically, Figure 1 A structural schematic diagram of a double-pass pre-chirp amplifier system provided in an embodiment of the present invention, wherein the double-pass pre-chirp amplifier system includes, in sequence along the optical path direction: a seed source 1, a circulator 2, a single-mode gain fiber 3, a long-period fiber grating 4, a laser combiner 6, a large-mode-field double-clad gain fiber 7, and a pre-chirp grating group 8. The laser is amplified twice in the large-mode-field double-clad gain fiber 7, which significantly improves the gain of the amplifier and the system efficiency, while effectively improving the signal-to-noise ratio of the signal and reducing the system noise.

[0042] Specifically, the seed source 1 used in this embodiment is a picosecond seed source, which is used to emit signal light with linear chirp. The seed source 1 provides signal light with linear chirp to provide a basis for subsequent amplification operations, and its chirp characteristics can provide a basis for subsequent pre-chirp management and other operations, which helps to achieve precise control and optimization of laser pulses.

[0043] The circulator 2 is used to receive the laser signal and output the laser signal to the single-mode gain fiber 3, ensuring that the laser signal can be transmitted in a predetermined optical path direction. The unidirectional transmission characteristic of the circulator 2 can avoid reverse transmission of the signal, ensuring the stability of the system and the accuracy of signal transmission.

[0044] The single-mode gain fiber 3 is used to perform a modulation on the signal light and output the modulated signal light to the long-period fiber grating 4. Through the single-mode gain fiber 3, the signal light can be preliminarily processed and optimized to a certain extent, providing a better signal basis for subsequent operations such as amplification and mode conversion. The modulated signal light is output to the long-period fiber grating 4 to prepare for subsequent mode conversion.

[0045] The long-period fiber grating 4 is used to perform a mode conversion on the signal light after the primary modulation, and output the signal light after the primary mode conversion to the large-mode-field double-clad gain fiber 7. By converting one mode of laser into another mode, such as converting the core fundamental mode into 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 signal light after mode conversion is output to the large-mode-field double-clad gain fiber 7, creating favorable conditions for the subsequent amplification process.

[0046] The pump source 5 is used to generate pump light to provide energy for the subsequent amplification process. The pump light is crucial for the population inversion in the large mode field double-clad gain fiber 7, and the pump source 5 provides key energy supply for achieving laser amplification.

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

[0048] The large mode field double-clad gain fiber 7 is used to amplify the signal light after the primary mode conversion and output the amplified signal light to the pre-chirp grating group 8. The large mode field double-clad gain fiber 7 amplifies the signal light after the primary mode conversion, thereby increasing the power of the laser. The large mode field double-clad gain fiber 7 has a larger mode field area, can withstand higher power, and reduces nonlinear effects. The amplified laser is output to the pre-chirp grating group 8, in preparation for further pre-chirp management and secondary amplification.

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

[0050] A double-pass pre-chirp amplification system provided in this 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 of the system and the laser quality, and utilizes the double-pass amplification technology, that is, the laser passes through the large-mode-field double-clad gain fiber 7 twice, which significantly improves the power and intensity of the output laser. Compared with the single-pass amplification system, it has a higher gain and improves the overall efficiency of the system. The characteristics of the laser pulse are optimized through the pre-chirp management of the pre-chirp grating group 8, and the chirped picosecond seed pulse is compressed to femtosecond, so as to prepare for improving the pulse peak power and exciting self-phase modulation in the subsequent amplification process, and finally achieve 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.

[0051] The dual-pass pre-chirp amplification system can be widely used in fields that require high-power, 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 (spectroscopy, ultrafast physical process research, etc.), etc., providing strong technical support for the development and progress of these fields.

[0052] As a further improvement of the present invention, the pre-chirp grating group 8 includes a first diffraction grating 81, a second diffraction grating 82 and a plane reflector 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-clad gain fiber 7, and the first diffraction grating 81 and the second diffraction grating 82 form a grating pair, and the distance between the grating pairs is adjusted to change the chirp amount of the incident laser pulse, and the chirp amount of the laser pulse is accurately adjusted to achieve accurate compression of the laser pulse from picoseconds to femtoseconds, realize pre-chirp management of the laser pulse, and improve the efficiency and quality of laser amplification.

[0053] Furthermore, the plane reflector 83 is placed perpendicular to the laser transmission direction, which ensures that the laser can be accurately reflected back to the large mode field double-clad gain fiber 7, making the double-pass amplification process more stable and efficient. During the pre-chirp management process, the plane mirror 83 reflects the laser light processed by the first diffraction grating 81 and the second diffraction grating 82 back to the original path, so that the laser light can enter the large mode field double-clad gain fiber 7 again. When the laser light is reflected back to the double-clad gain fiber, the laser light can obtain energy again to achieve secondary amplification. By reflecting the laser light back to the original optical path, the laser light can pass through the previous optical element and gain fiber again, thereby further adjusting and optimizing its characteristics, and finally achieving higher quality and higher power laser output. At the same time, the laser light processed by the pre-chirp grating group 8 can better suppress nonlinear effects and noise during the secondary amplification process, because its pulse characteristics are optimized, which is more conducive to efficient absorption and amplification of energy, thereby significantly improving the power and intensity of the output secondary amplified laser light. The pre-chirp grating group 8 composed of the grating pair and the plane mirror 83 compresses the chirped picosecond seed source into a femtosecond pulse, 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 present invention, the dual-pass pre-chirp amplification system further includes an isolator 9, and the circulator 2 includes a first end 21, a second end 22, and a third end 23; the first end 21 of the circulator 2 is connected to 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 to the seed source 1 through the isolator 9, and the pump light and the secondary amplified laser are effectively isolated by utilizing the characteristics of the isolator 9 to prevent the pump light and the secondary amplified laser from returning to the seed source 1, and to avoid the pump light and the high-energy secondary amplified laser from flowing back to the seed source 1 to damage the seed source 1, affecting the performance and life of the seed source 1, and effectively avoiding system failure. The service life of the seed source 1 is extended, and the stable operation of the entire system is guaranteed.

[0055] Furthermore, the second end 22 of the circulator 2 is connected to the single-mode gain fiber 3; the second end 22 of the circulator is connected to 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, so as to perform a modulation on the signal light, thereby ensuring the orderly flow of the laser in the system, and preparing for the subsequent mode conversion of the long-period fiber grating 4 and the amplification process of the large-mode-field double-clad gain fiber 7.

[0056] Specifically, the third end 23 of the circulator 2 is used to output the laser after the second amplification. The third end 23 of the circulator serves as the output end of the system and is used to output the laser after the second amplification. After a series of processing, including modulation of the single-mode gain fiber 3, mode conversion of the long-period fiber grating 4, double-pass amplification of the large-mode-field double-clad gain fiber 7, and pre-chirp management of the pre-chirp grating group 8, the laser after the second amplification is finally output from the third end 23 of the circulator 2, providing a high-quality laser signal for subsequent applications.

[0057] As a further improvement of the present invention, the double-pass pre-chirp amplification system further includes a half-wave plate, which is located between the large mode field double-clad gain fiber 7 and the pre-chirp grating group 8 along the optical path direction, and is used to adjust the polarization state of the laser. By arranging a half-wave plate 10 between the large mode field double-clad gain 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 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, thereby more effectively pre-chirping the laser pulse, ensuring the pulse compression of the laser and the quality of the final output laser, and improving the performance and efficiency of the entire system.

[0058] As a further improvement of the present invention, the single-mode gain fiber 3 modulates the signal light once, specifically: the single-mode gain fiber 3 converts the signal light from multi-mode to the core fundamental mode. The single-mode gain fiber 3 modulates the signal light once, specifically converts the laser signal from multi-mode to the core fundamental mode. When the multi-mode signal light propagates in the optical fiber, it will produce mode dispersion 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 subsequent processing. When the single-mode gain fiber 3 converts the signal light into the core fundamental mode, only one mode is allowed to propagate in the optical fiber, avoiding the mode dispersion problem caused by multi-mode propagation, and significantly improving the quality of the laser signal. Since the mode dispersion caused by multi-mode 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 present invention, the long-period fiber grating 4 performs a mode conversion on the signal light after the first modulation, specifically: the long-period fiber grating 4 converts the signal light from the core fundamental mode to the cladding mode. The long-period fiber grating 4 converts the signal light after the first modulation of the single-mode gain fiber 3 from the core fundamental mode to the cladding mode, and its main purpose is to increase the mode field area. The mode field area of ​​the core fundamental mode is relatively small. When the input power is high, it is easy to cause nonlinear effects such as stimulated Brillouin scattering and stimulated Raman scattering. These nonlinear effects will reduce the output power of the signal light, cause spectral broadening and pulse distortion, and limit the performance improvement of the system. Converting the signal light into the cladding mode can effectively increase the mode field area and reduce the optical power density, thereby inhibiting the occurrence of nonlinear effects. In a high-power fiber laser system, a smaller mode field area will concentrate the light field energy and easily reach the threshold of the nonlinear effect. The cladding mode has a larger mode field area, and the light energy is more dispersed in the cladding, which reduces the light field intensity, thereby avoiding the generation of nonlinear effects or reducing the impact of nonlinear effects on the system. The signal light is converted from the core fundamental mode to the cladding mode through the long-period fiber grating 4, which significantly reduces the nonlinear effects that may occur in the system, improves the stability and reliability of the system, avoids energy loss and laser quality degradation caused by nonlinear effects, reduces the occurrence of nonlinear effects, and improves the power bearing capacity of the system. The signal light after conversion into the cladding mode enters the large-mode-field double-cladding gain fiber 7, and the large-mode-field gain fiber can use the light field in the cladding to perform amplification operations. Since the mode field area of ​​the cladding mode is large, the large-mode-field double-cladding gain fiber 7 can more effectively achieve particle number inversion and amplification of optical signals while avoiding fiber damage, laying the foundation for achieving higher amplification gain and better laser output.

[0060] As a further improvement of the present invention, the laser undergoes secondary amplification, specifically including: the large mode field double-clad gain fiber 7 performs secondary amplification on the amplified laser; the long period fiber grating 4 performs secondary mode conversion on the secondary amplified laser; the long period fiber grating 4 performs secondary mode conversion on the secondary amplified laser; the single mode gain fiber 3 performs secondary modulation on the secondary mode converted laser.

[0061] Specifically, the large mode field double-clad gain fiber 7 performs secondary amplification on the amplified laser. The large mode field double-clad gain fiber 7 plays an important amplification function in the system. During the secondary amplification process, it receives the laser that has been processed and reflected by the pre-chirped grating group 8, and amplifies it again. Since the large mode field double-clad gain fiber 7 has a large mode field area and a special double-clad structure, it can more effectively utilize the energy provided by the pump light and provide sufficient gain for the laser that has been amplified twice. 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 field double-clad gain fiber 7 performs secondary amplification on the laser through the gain medium and pump light inside it, so that the energy of the laser is further enhanced, providing a stronger energy basis for subsequent processing and final output.

[0062] Furthermore, 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-field 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. The laser after secondary amplification is adjusted to a mode that is more conducive to the processing of the single-mode gain fiber 3, preparing for the subsequent secondary modulation, and at the same time, it can further suppress the nonlinear effect and ensure the stability and performance of the system.

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

[0064] The combination of secondary amplification, secondary mode conversion and secondary modulation improves the output power of the system as a whole. Through the secondary amplification of the large mode field double-clad gain fiber 7, the output power of the system is significantly improved, meeting the requirements for 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 the quality and performance of the laser are optimized while the power is increased. 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 present invention, the long-period fiber grating 4 performs secondary mode conversion on the secondary amplified laser, specifically: the long-period fiber grating 4 converts the secondary amplified laser from the cladding mode to the core fundamental mode. The long-period fiber grating 4 converts the secondary amplified laser into the core fundamental mode to provide a 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, which is conducive to obtaining a high-quality output beam. Conversion to the core fundamental mode prepares for single-mode output, ensuring that the system can eventually achieve high-quality single-mode output through 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 field double-cladding gain fiber 7, converts the secondary amplified cladding mode laser into the core fundamental mode, and provides an ideal input for the subsequent secondary modulation of the single-mode gain fiber 3. Ensure the coherence and efficiency of the system from secondary amplification to final output. The single-mode gain optical fiber 3 can further perform signal modulation based on the converted core fundamental mode to optimize the time, space and spectral characteristics of the signal so that the final output laser meets the performance requirements of various application scenarios.

[0066] As a further improvement of the present invention, the single-mode gain fiber 3 performs secondary modulation on the laser of the secondary mode conversion, specifically: the single-mode gain fiber 3 increases the peak power of the laser of the secondary amplification to achieve self-phase modulation, so that the laser spectrum of the secondary amplification of the core fundamental mode is broadened. The single-mode gain fiber 3 performs secondary modulation on the laser after the secondary mode conversion, specifically performs self-phase modulation. During the secondary amplification process, due to factors such as the saturation effect of the gain medium, the gain narrowing phenomenon will be introduced. The spectrum broadening achieved by the single-mode gain fiber 3 through the self-phase modulation of the secondary amplified laser of the core fundamental mode can compensate for this gain narrowing. After the self-phase modulation compensation of the single-mode gain fiber 3, the system can maintain a wider spectrum, ensuring that the laser still has good performance at high power output, such as shorter pulse width, higher peak power and better time and space resolution.

[0067] As a further improvement of the present invention, the second diffraction grating 82 is mounted on an adjustable displacement platform. By mounting 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 in 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 it and the first diffraction grating 81 can be adjusted, thereby affecting their diffraction and interference effects on the laser pulse, and achieving precise control of the chirp amount of the laser pulse, which is crucial for compressing the chirped picosecond seed pulse to femtosecond. Different spacings will lead to different chirp compensation effects, so that the laser pulse can be compressed to the required ultrashort pulse width as needed, providing conditions for the system to output high-quality ultrashort pulse lasers, and helping to achieve overall optimization of the system from high-power amplification to high-quality pulse output.

[0068] The technical features of the above embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0069] The above embodiments only express the preferred implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent application. It should be pointed out that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the attached claims.

Claims

1. A dual-pass pre-chirp amplification system, characterized in that: Along the optical path direction, it includes: A seed source, used for emitting a signal light with a linear chirp; A circulator, used for receiving the signal light and outputting the signal light to a single-mode gain optical fiber; A single-mode gain optical fiber, used for performing a primary modulation on the signal light and outputting the primary modulated signal light to a long-period fiber grating; A long period fiber grating, used for performing a mode conversion on the signal light after the primary modulation, and outputting the signal light after the primary mode conversion to a large mode field double-clad gain optical fiber; A pump source, used to generate pump light; Laser beam combiner, used to couple pump light into large mode area double-clad gain fiber; A large mode field double-clad gain optical fiber, used for amplifying the signal light after the primary mode conversion, and outputting the amplified laser to the pre-chirped grating group; The pre-chirp grating group is used to perform pre-chirp management on the amplified laser and reflect the amplified laser back to the original path. The laser is output from the circulator after secondary amplification.

2. The dual-pass pre-chirp amplification system according to claim 1, characterized in that: The pre-chirp grating group includes a first diffraction grating, a second diffraction grating and a plane reflector; The first diffraction grating is arranged in parallel with the second diffraction grating; The plane reflecting mirror is placed perpendicular to the laser transmission direction.

3. The dual-pass pre-chirp amplification system according to claim 1, characterized in that: The dual-pass pre-chirp amplification system further includes an isolator, and the circulator includes 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 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; The second end of the circulator is connected to the single-mode gain optical fiber; The third end of the circulator is used to output the laser after the second amplification.

4. The dual-pass pre-chirp amplification system according to claim 1, characterized in that: The double-pass pre-chirp amplification system also includes a half-wave plate, which is located between the large mode field double-clad gain fiber and the pre-chirp grating group along the optical path direction and is used to adjust the polarization state of the laser.

5. The dual-pass pre-chirp amplification system according to claim 1, characterized in that: The single-mode gain optical fiber performs a modulation on the laser signal, specifically: the single-mode gain optical fiber converts the signal light from multi-mode to core fundamental mode.

6. The dual-pass pre-chirp amplification system according to claim 1, characterized in that: The long period fiber grating performs a mode conversion on the signal light after the primary modulation, specifically: the long period fiber grating converts the signal light from the core fundamental mode to the cladding mode.

7. The dual-pass pre-chirp amplification system according to claim 1, characterized in that: The laser is subjected to secondary amplification, specifically comprising: The large mode field double-clad gain optical fiber performs secondary amplification on the amplified laser; The long period fiber grating performs secondary mode conversion on the secondary amplified laser; The single-mode gain optical fiber performs secondary modulation on the laser light subjected to secondary mode conversion.

8. The dual-pass pre-chirp amplification system according to claim 7, characterized in that: The long-period fiber grating performs secondary mode conversion on the secondarily amplified laser light, specifically: the long-period fiber grating converts the secondarily amplified laser light from a cladding mode into a core fundamental mode.

9. The dual-pass pre-chirp amplification system according to claim 7, characterized in that: The single-mode gain optical fiber performs secondary modulation on the secondary mode converted laser, specifically: the single-mode gain optical fiber performs self-phase modulation on the secondary amplified laser to broaden the secondary amplified laser spectrum of the core fundamental mode.

10. The dual-pass pre-chirp amplification system according to claim 2, characterized in that: The second diffraction grating is installed on an adjustable displacement platform.

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