A dispersion-managed femtosecond all-fiber laser with adjustable pulse width

Abstract

The invention discloses a dispersion-managed femtosecond all-fiber laser with adjustable pulse width, which has low cost, simple structure, stable operation, high power, and adjustable pulse width and repetition frequency. A fiber laser oscillator, a pulse stretcher, a selector, and a pulse laser amplifier are all connected by optical fibers. The fiber laser oscillator adopts a linear short cavity structure and an extracavity pumping method. The output end of the fiber laser oscillator is connected to the input end of the pulse stretcher, the output end of the pulse stretcher is connected to the input end of the selector, and the output end of the selector is connected to the input end of the pulse laser amplifier. The fiber laser oscillator generates a wide-spectrum mode-locked pulse laser. The pulse stretcher stretches the pulse width of the laser to the order of hundreds of picoseconds. The laser repetition frequency is tuned by the selector. After the laser is power-amplified by a first-stage pre-amplifier and a second-stage main amplifier, it enters a pulse compressor to compress the output pulse laser width to the order of femtoseconds.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber lasers, and in particular to a dispersion-managed femtosecond all-fiber laser with adjustable pulse width. Background Art

[0002] With the rapid development of laser technology, ultrafast lasers have appeared in people's vision. Ultrafast lasers play an increasingly important role in people's modern work and life, and have great economic value and social benefits. High-power ultrashort pulse fiber lasers have the advantages of good beam quality, high thermal stability, wide gain bandwidth, high peak power, compact structure, low cost, "cold" burning of materials, and no maintenance. They are widely used in industrial material processing, biomedicine, supercontinuum generation, and remote sensing measurement, and have become a research hotspot in recent years.

[0003] At present, the methods for achieving mode locking are mainly divided into two types: active mode locking based on intracavity phase or amplitude modulation and passive mode locking based on saturable absorption effect. Active mode locking can easily achieve repetition frequency tuning and obtain higher pulse repetition frequency, but its structure is relatively complex and the narrowest pulse width that can be obtained is limited by the modulation system.

[0004] Based on the passive mode-locking principle, the following three methods are currently used most: First, the nonlinear amplifying ring mirror (NALM) mode-locked fiber laser, the principle of which is to generate two beams of light that are transmitted in opposite directions in a polarization-maintaining fiber loop, and interfere in a beam splitter, and use the nonlinear phase shift of the two beams of light to control the transmittance of light of different intensities to achieve saturable absorption characteristics, and it is easy to obtain ultra-short pulse lasers with a wide spectrum. However, this type of fiber NALM mode-locked laser has problems such as high production cost, high pump power consumption, and difficulty in mode locking. The second is the nonlinear polarization rotation (NPE) mode-locked fiber laser, which has low cost, easy to adjust parameters, and easy to adjust the net cavity dispersion to obtain a wide spectrum of mode-locked pulses, but it usually needs to be constructed using non-polarization-maintaining fiber and spatial grating structure, which makes it very sensitive to environmental changes. External temperature, vibration, and other disturbances will affect the operating state of the laser and the output pulse characteristics, and the structure is relatively complex, making it difficult to achieve full fiberization. These shortcomings limit its practical application. The third is the semiconductor saturable absorber (SESAM) mode-locked fiber laser, which uses the semiconductor saturable absorption effect to achieve mode locking. This type of mode-locked laser can achieve a higher repetition frequency, with a simple structure, low mode-locking threshold, and good stability. However, compared with the first two mode-locking methods, it is difficult to obtain a mode-locked pulse laser with a wide spectral bandwidth. Its mode-locking spectral bandwidth is generally several nanometers or even less than one nanometer, which limits its application development in femtosecond pulse lasers.

[0005] Therefore, how to provide a high-power femtosecond all-fiber laser with low cost, simple structure, stable operation, adjustable pulse width and repetition frequency as a seed source for high-power and high-energy femtosecond lasers has become an important issue that needs to be urgently solved by technicians in this field. Summary of the invention

[0006] In order to overcome the defects of the prior art, the technical problem to be solved by the present invention is to provide a dispersion managed pulse width adjustable femtosecond all-fiber laser, which has low cost, simple structure, stable operation, high power, and adjustable pulse width and repetition frequency.

[0007] The technical solution of the present invention is: the dispersion-managed pulse width adjustable femtosecond all-fiber laser comprises: a mode-locked light source (27) composed of a fiber laser oscillator (7), a pulse stretcher (10) and a selector (15), a pulse laser amplifier (26) and a pulse compressor (28);

[0008] The fiber laser oscillator, pulse stretcher, selector and pulse laser amplifier are all connected via optical fibers. The fiber laser oscillator adopts a linear short cavity structure and an extracavity pumping method. The output end of the fiber laser oscillator is connected to the input end of the pulse stretcher. The pulse stretcher includes a fiber circulator (8) and a second chirped fiber Bragg grating (9). The central wavelength of the second chirped fiber Bragg grating is in the range of 1020nm to 1040nm. The output end of the pulse stretcher is connected to the input end of the selector. The selector includes a fiber acousto-optic modulator (11), a light detector (12), a radio frequency driver (13), a pulse selector (14), the output end of the selector is connected to the input end of a pulse laser amplifier, and the pulse laser amplifier includes a first-stage pre-amplification part (20) and a second-stage main amplification part (25); the fiber laser oscillator generates a wide-spectrum mode-locked pulse laser, and the pulse stretcher stretches the pulse width of the laser to the order of hundreds of picoseconds. The laser repetition frequency is tuned by the selector, and the laser is power-amplified by the first-stage pre-amplification part and the second-stage main amplification part before entering the pulse compressor to compress the output pulse laser width to the order of femtoseconds.

[0009] The present invention is a fiber laser resonant cavity composed of a chirped fiber Bragg grating and a semiconductor saturable absorber. Due to the characteristics of the chirped fiber Bragg grating, the positive dispersion introduced by the single-mode fiber in the resonant cavity can be compensated, so that the net cavity dispersion in the resonant cavity approaches zero, thereby obtaining a mode-locked pulse laser with a wide spectral bandwidth, solving the problem of narrow spectral bandwidth of the traditional SESAM mode-locked laser, and compared with other passive mode-locked lasers, the cost is low, the structure is simple, the stability is high, and the output pulse width is smaller. After the mode-locked pulse laser is pulse-broadened and frequency-selected by the large-dispersion chirped fiber Bragg grating, the influence of the nonlinear effect on the power increase is effectively suppressed, and the repetition frequency is tunable, which can greatly improve the single pulse energy output by the laser, and after passing through the pulse compressor, the pulse width can be compressed to the femtosecond level and the pulse width can be tuned, providing a good seed source for subsequent further fiber laser amplification or solid laser amplification and compression of femtosecond pulses. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a schematic diagram of the principle structure of the dispersion-managed femtosecond all-fiber laser with adjustable pulse width according to the present invention.

[0011] Figure 2 Schematic diagram of the structure of a pulse laser amplifier according to the present invention.

[0012] Figure 3 This is a test result diagram of the laser output spectrum of the dispersion-managed, pulse-width-adjustable femtosecond all-fiber laser according to the present invention.

[0013] Figure 4 This is a graph showing the test results of the mode-locked laser output pulse width of the dispersion-managed femtosecond all-fiber laser with adjustable pulse width according to the present invention.

[0014] Figure 5 This is a graph showing the test results of the laser output pulse width of the dispersion-managed, pulse-width-adjustable femtosecond all-fiber laser according to the present invention.

[0015] Figure 6 This is a graph showing the repetition rate test results of the mode-locked laser output of the dispersion-managed, pulse-width-adjustable femtosecond all-fiber laser according to the present invention. DETAILED DESCRIPTION

[0016] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0017] It should be noted that the term "comprises" and any variations in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, apparatus, product or equipment that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products or equipment.

[0018] like Figure 1 As shown, this dispersion-managed pulse width adjustable femtosecond all-fiber laser comprises: a mode-locked light source 27 composed of a fiber laser oscillator 7, a pulse stretcher 10 and a selector 15, a pulse laser amplifier 26 and a pulse compressor 28;

[0019] The fiber laser oscillator, pulse stretcher, selector and pulse laser amplifier are all connected through optical fiber. The fiber laser oscillator adopts a linear short cavity structure and an extracavity pumping method. The output end of the fiber laser oscillator is connected to the input end of the pulse stretcher. The pulse stretcher includes a fiber circulator 8 and a second chirped fiber Bragg grating 9. The central wavelength of the second chirped fiber Bragg grating is in the range of 1020nm~1040nm. The output end of the pulse stretcher is connected to the input end of the selector. The selector includes a fiber acousto-optic modulator 11, an optical detector The detector 12, the RF driver 13, the pulse selector 14, the output end of the selector is connected to the input end of the pulse laser amplifier, the pulse laser amplifier includes a first-stage pre-amplification part 20 and a second-stage main amplification part 25; the fiber laser oscillator generates a wide-spectrum mode-locked pulse laser, the pulse stretcher stretches the pulse width of the laser to the order of hundreds of picoseconds, the laser repetition frequency is tuned by the selector, the laser is power-amplified by the first-stage pre-amplification part and the second-stage main amplification part, and then enters the pulse compressor to compress the output pulse laser width to the order of femtoseconds.

[0020] The present invention is a fiber laser resonant cavity composed of a chirped fiber Bragg grating and a semiconductor saturable absorber. Due to the characteristics of the chirped fiber Bragg grating, the positive dispersion introduced by the single-mode fiber in the resonant cavity can be compensated, so that the net cavity dispersion in the resonant cavity approaches zero, thereby obtaining a mode-locked pulse laser with a wide spectral bandwidth, solving the problem of narrow spectral bandwidth of the traditional SESAM mode-locked laser, and compared with other passive mode-locked lasers, the cost is low, the structure is simple, the stability is high, and the output pulse width is smaller. After the mode-locked pulse laser is pulse-broadened and frequency-selected by the large-dispersion chirped fiber Bragg grating, the influence of the nonlinear effect on the power increase is effectively suppressed, and the repetition frequency is tunable, which can greatly improve the single pulse energy output by the laser, and after passing through the pulse compressor, the pulse width can be compressed to the femtosecond level and the pulse width can be tuned, providing a good seed source for subsequent further fiber laser amplification or solid laser amplification and compression of femtosecond pulses.

[0021] Preferably, the fiber laser oscillator comprises a semiconductor saturable absorber SESAM 1, a first gain fiber 2, a first chirped fiber Bragg grating 3, a first wavelength division multiplexer 4, a first fiber isolator 5 and a first pump source 6;

[0022] The first end of the first gain fiber is connected to the semiconductor saturable absorber, and the second end of the first gain fiber is connected to the first end of the first chirped fiber Bragg grating; the second end of the first chirped fiber Bragg grating is connected to the output end of the first wavelength division multiplexer, the output end of the first pump source is connected to the pump input end of the first wavelength division multiplexer, and the input end of the first wavelength division multiplexer is connected to the input end of the first optical fiber isolator.

[0023] Preferably, the pigtails of the passive devices in the fiber laser oscillator are all polarization-maintaining fibers, and the dispersion of the polarization-maintaining fibers in the central band of the fiber Bragg grating is positive dispersion; the dispersion of the first gain fiber in the central band of the fiber Bragg grating is positive dispersion.

[0024] Preferably, the first wavelength division multiplexer is located outside the laser resonant cavity, and couples the pump light output by the pump source into the fiber laser oscillator.

[0025] Preferably, a resonant cavity is formed by using a dispersion management method, using a SESAM and a first chirped fiber Bragg grating 3 as cavity mirrors, wherein the first chirped fiber Bragg grating uses a temperature control method to control the second-order negative dispersion provided to compensate for the second-order positive dispersion brought by the optical fiber in the resonant cavity, so that the net cavity dispersion approaches zero, and the first chirped fiber Bragg grating is partially transmitted as an output coupling mirror.

[0026] Preferably, the semiconductor saturable absorber SESAM is packaged in the form of optical fiber.

[0027] Preferably, the first-stage preamplifier part includes a second wavelength division multiplexer 16, a second gain fiber 17, a second pump source 18 and a second fiber isolator 19; the input end of the second wavelength division multiplexer is connected to the output end of the fiber acousto-optic modulator, the output end of the second pump source is connected to the pump input end of the second wavelength division multiplexer, the output end of the second wavelength division multiplexer is connected to the first end of the second gain fiber, the second end of the second gain fiber is connected to the input end of the second fiber isolator, and the output end of the second fiber isolator is connected to the second-stage main amplifier part, wherein the pigtails of the passive components of most of the first-stage preamplifiers are polarization-maintaining fibers.

[0028] Preferably, the secondary main amplification part includes a beam combiner 21, a third gain fiber 22, a third pump source 23 and a third fiber isolator 24; the input end of the beam combiner is connected to the output end of the primary prevention part, the output end of the third pump source is connected to the pump input end of the beam combiner, the output end of the beam combiner is connected to the first end of the third gain fiber, the second end of the third gain fiber is connected to the input end of the third fiber isolator, and the output end of the third fiber isolator is used to output the amplified pulsed laser beam; wherein the third pump source is a multimode pump, and the third gain fiber is a double-clad ytterbium-doped gain fiber.

[0029] Preferably, the high-power multimode pump source of the secondary main amplifier part adopts a semiconductor laser with a wavelength of 976nm, and the beam combiner uses the pump light of the high-power multimode pump source to pump the third gain fiber through cladding pumping.

[0030] Preferably, the high-power pulse laser output by the pulse laser amplifier enters a pulse compressor to compress the pulse width of the output pulse laser to femtosecond level, and tune the pulse width by adjusting the dispersion amount.

[0031] The present invention is described in more detail below.

[0032] like Figure 1As shown, it includes a mode-locked light source 27 composed of a fiber laser oscillator 7, a pulse stretcher 10 and a selector 11, a pulse laser amplifier 26 and a pulse compressor 28. The fiber laser oscillator 7, the pulse stretcher 10, the selector 15 and the pulse laser amplifier 26 are all connected by optical fibers. The fiber laser oscillator 7 adopts a linear short cavity structure. The output end of the fiber laser oscillator 7 is connected to the input end of the pulse stretcher 10. The pulse stretcher 10 is composed of a fiber circulator 8 and a second chirped fiber Bragg grating 9. The output end of the pulse stretcher 10 is connected to the input end of the selector 15. The selector 15 is composed of a fiber acousto-optic modulator 11, a light detector 12, a radio frequency driver 13 and a pulse selector 14. The output end of the selector 15 is connected to the input end of the pulse laser amplifier 26. The amplifier 26 includes a first-stage pre-amplifier 20 and a second-stage main amplifier 25. The output end of the pulse laser amplifier 26 is connected to the input end of the pulse compressor; the fiber laser oscillator 7 generates a wide-spectrum mode-locked pulse laser, and the pulse stretcher 10 stretches the pulse width of the laser to the order of hundreds of picoseconds, and then the laser repetition frequency is tuned through the menu selector 15, and then the laser is power-amplified through the first-stage pre-amplifier 20 and the second-stage main amplifier 25, and finally enters the pulse compressor 28 to compress the pulse width to the order of femtoseconds, and can be tuned. Thus, a stable, wide-spectrum bandwidth, high-power femtosecond pulse laser is output. Wherein, the central wavelength of the chirped fiber Bragg grating 3 is in the range of 1020nm~1040nm.

[0033] Further, the fiber laser oscillator 7 comprises a semiconductor saturable absorber 1, a first gain fiber 2, a first chirped fiber Bragg grating 3, a first wavelength division multiplexer 4, a first fiber isolator 5 and a first pump source 6; the first end of the first gain fiber 2 is connected to the semiconductor saturable absorber 1, and the second end of the first gain fiber 2 is connected to the first end of the chirped fiber Bragg grating 3; the second end of the chirped fiber Bragg grating 3 is connected to the output end of the first wavelength division multiplexer 4, the output end of the first pump source 6 is connected to the pump input end of the first wavelength division multiplexer 4, and the common end of the first wavelength division multiplexer 4 is connected to the input end of the first fiber isolator 5;

[0034] Specifically, in the actual composition of the fiber laser oscillator 7, the first wavelength division multiplexer 4 is located outside the laser resonant cavity composed of the semiconductor saturable absorber 1, the first gain fiber 2 and the first chirped fiber Bragg grating 3, and is used to couple the pump light output by the first pump source 6 into the fiber laser oscillator, thereby reducing the number of devices used in the resonant cavity and improving the stability of the overall fiber laser oscillator 7. At the same time, it is more conducive to achieving the regulation of the amount of dispersion in the cavity and the control of the repetition frequency.

[0035] Specifically, the output transmission percentage of the chirped fiber Bragg grating 3 in the fiber laser oscillator 7 can be adjusted to adjust the output power, but the output percentage of the chirped fiber Bragg grating 3 needs to be coordinated with the length of the first gain fiber 2. The chirped fiber Bragg grating 3 can effectively compensate for the dispersion in the fiber laser oscillator 7 to achieve ultrashort pulse laser output with a narrow pulse width, and effectively control the central wavelength of the output laser and the spectral bandwidth of the mode-locked laser through its filtering effect, reduce noise, and improve system stability; the chirped fiber Bragg grating 3 partially transmits and can be used as an output coupling mirror.

[0036] Specifically, the semiconductor saturable absorber 1 in the fiber laser oscillator 7 is fiber-optically packaged, which effectively avoids the instability of the mode-locking system caused by the spatial structure and realizes all-fiber semiconductor saturable absorber mode locking.

[0037] Specifically, the first pump source 6 outputs pump light, and the pump light enters the fiber laser oscillator 7 from the pump input end of the first wavelength division multiplexer 4. The first gain fiber 2 absorbs the pump light and performs gain. The light output by the first gain fiber 2 is incident on the semiconductor saturable absorber 1, and the semiconductor saturable absorber 1 compresses the pulse width of the pulse incident therein. The compressed pulse passes through the semiconductor saturable absorber 1 and then reflects back along the optical path to the first fiber grating 3 at the other end of the fiber laser oscillator 7. The first chirped fiber Bragg grating 3 filters the incident light and compensates for positive dispersion, and reflects a light beam in a wavelength band corresponding to the central wavelength, and the light beam is then The light is incident on the first gain fiber 2 for the second time, the first gain fiber 2 absorbs the light beam in a specific wavelength band and performs gain on the light beam incident therein, the light output by the first gain fiber 2 is incident on the semiconductor saturable absorber 1 again, and the above process is repeated, the light is repeatedly reflected in the fiber laser oscillator 7, most of the light is absorbed by the semiconductor saturable absorber 1, and the remaining light forms a stable locked mode and enters the pulse stretcher 10, the selector 15 and the pulse laser amplifier 26 through the second end of the first fiber grating 3 through the first wavelength division multiplexer 4 for amplification, thereby outputting an ultrashort pulse laser with high power, narrow pulse width, wide spectral bandwidth and adjustable repetition rate.

[0038] Specifically, all components of the fiber laser oscillator 7 are polarization-maintaining components to ensure that the system can operate stably and realize a short-cavity low-threshold mode-locked femtosecond pulse fiber laser with self-starting performance.

[0039] Optionally, the pulse stretcher 10 includes a fiber circulator 8 and a second chirped fiber Bragg grating 9; the output end of the first fiber isolator 5 is connected to the first end of the fiber circulator 8, and the second end of the fiber circulator 8 is connected to the input end of the second chirped fiber Bragg grating 9.

[0040] Specifically, the central wavelength, bandwidth and reflectivity of the second chirped fiber Bragg grating 9 can be set according to the output laser parameter requirements of the laser to achieve the adjustment and control of the pulse width after broadening. In this embodiment, the pulse width of the laser is broadened to hundreds of picoseconds, and the dispersion amount provided by the second chirped fiber Bragg grating 9 needs to be matched according to the spectral bandwidth of the output laser to achieve the tuning of the broadened pulse width.

[0041] Specifically, the pulse stretcher 10 is composed of a fiber circulator 8 and a second chirped fiber Bragg grating 9. The pulse laser output by the fiber laser oscillator 7 enters from the first end of the fiber circulator 8, is output from the second end of the fiber circulator 8 and enters the second chirped fiber Bragg grating 9, and then is reflected by the second chirped fiber Bragg grating 9, returns to the second end of the fiber circulator 8 along the original path and is output from the third end of the fiber circulator 8, thereby completing the stretching of the pulse width. Among them, the light of different spectral components of the laser propagates in the second chirped fiber Bragg grating 9 with different optical paths, with long waves in front and short waves in the back, resulting in the stretching of the pulse width, reducing the peak power of the pulse laser. In the fiber amplifier, the influence of nonlinear effects on the power increase can be effectively weakened, thereby obtaining a pulse laser with high average power.

[0042] Furthermore, the menu selector 15 includes a fiber acousto-optic modulator 11, a light detector 12, a radio frequency driver 13 and a pulse selector 14; the input end of the fiber acousto-optic modulator 11 is connected to the third end of the fiber circulator 8; the light detector 12 is connected to the input end of the pulse selector 14, the output end of the pulse selector 14 is connected to the input end of the radio frequency driver 13, the output end of the radio frequency driver 13 is connected to the electrical signal input end of the fiber acousto-optic modulator 11, and the fiber laser oscillator 7 outputs a mode-locked laser pulse signal to be transmitted to the light detector 12.

[0043] Specifically, the selector 15 requires the pulse selector 14 to set the repetition frequency of the pulse selection signal according to the repetition frequency of the mode-locked pulse signal of the fiber laser oscillator 7, and then send the set pulse selection signal to the RF driver 13 to drive the fiber acousto-optic modulator 11 to modulate the repetition frequency of the mode-locked pulse laser. Among them, the repetition frequency of the pulse selection signal can be flexibly set according to the parameters of the output laser, so that the output laser repetition frequency can be adjusted and controlled within the repetition frequency range of the mode-locked pulse laser. After the mode-locked pulse laser is down-converted and then amplified by the fiber amplifier, the single pulse energy of the pulse laser can be significantly improved, thereby obtaining a high-energy pulse laser output in the optical fiber.

[0044] Further, Figure 2 A schematic diagram of the structure of a pulse laser amplifier provided by an embodiment of the present invention is shown in FIG. Figure 2 As shown, the pulse laser amplifier 26 includes a first-stage pre-amplifier part 20 and a second-stage main amplifier part 25 connected in sequence; the input end of the first-stage pre-amplifier part 20 is connected to the output end of the fiber acousto-optic modulator 11.

[0045] Specifically, the seed light output by the fiber laser oscillator 7 is amplified in the second stage by the pulse laser amplifier 26 to achieve a higher power output.

[0046] Further, refer to Figure 2 The first-stage preamplifier 20 includes a second wavelength division multiplexer 16, a second gain fiber 17, a second pump source 18, and a second fiber isolator 19; the common end of the second wavelength division multiplexer 16 is connected to the output end of the fiber acousto-optic modulator 11, the output end of the second pump source 18 is connected to the pump input end of the second wavelength division multiplexer 16, the output end of the second wavelength division multiplexer 16 is connected to the first end of the second gain fiber 17, the second end of the second gain fiber 17 is connected to the input end of the second fiber isolator 19, and the output end of the second fiber isolator 19 is connected to the second-stage main amplifier 25. The pigtails of the passive components of the first-stage preamplifier 20 are all polarization-maintaining fibers.

[0047] Specifically, the seed light after broadening and frequency selection is injected into the primary prevention part 20, and the second pump source 18 inputs the pump light to the second wavelength division multiplexer 16, so as to pump the second gain fiber 17. When the seed light passes through the second wavelength division multiplexer 16 and the second gain fiber 17, the second gain fiber 17 absorbs the light of a specific wavelength and outputs the light beam incident therein after gaining it, and the light beam output by the second gain fiber 17 is injected into the secondary main amplification part 25 through the second fiber isolator 19. In specific implementation, by controlling the pump power of the second pump source 18, the length of the second gain fiber 17, the absorption coefficient and other parameters, the spontaneous radiation can be effectively suppressed, the power can be amplified to the order of hundreds of milliwatts, and sufficient pulse signal light can be provided to enter the secondary main amplification part 25.

[0048] Furthermore, the secondary main amplification part 25 includes a beam combiner 21, a third gain fiber 22, a third pump source 23 and a third fiber isolator 24; the input end of the beam combiner 21 is connected to the output end of the primary prevention part 20, the output end of the third pump source 23 is connected to the pump input end of the beam combiner 21, the output end of the beam combiner 21 is connected to the first end of the third gain fiber 22, the second end of the third gain fiber 22 is connected to the input end of the third fiber isolator 24, and the output end of the third fiber isolator 24 is used to output the amplified pulse laser beam; wherein the pigtails of the passive components of the pulse laser amplifier 26 are all polarization-maintaining fibers. The third pump source is a multimode pump, and the third gain fiber is a double-clad ytterbium-doped gain fiber.

[0049] Specifically, the high-power multimode pump source of the secondary main amplifier part 25 adopts a semiconductor laser with a wavelength of 976nm, and the third gain fiber 22 has a high absorption efficiency of the pump light of this wavelength, which can effectively improve the optical-to-optical conversion efficiency of the output laser. The beam combiner 21 pumps the pump light of the high-power multimode pump source through cladding pumping to pump the third gain fiber 22, thereby obtaining a high-power ultrashort pulse laser output.

[0050] Optionally, the pulse laser amplifier 26 may be a multi-stage amplifier, and the actual composition may be set according to the output laser power requirement. In specific implementation, optical transmission may be achieved between multiple components in the laser by pigtail fusion.

[0051] Furthermore, the high-power pulse laser output by the pulse laser amplifier 26 enters the pulse compressor 28 to compress the pulse width of the output pulse laser.

[0052] Specifically, the pulse compressor 28 provides negative second-order dispersion to compensate for the positive second-order dispersion introduced by the pulse stretcher 10, and compresses the pulse width to femtosecond level. By adjusting the second-order dispersion introduced by the pulse compressor 28, the amplified pulse width can be tuned.

[0053] Figure 3 This is a test result diagram of the laser output spectrum of the dispersion-managed pulse-width adjustable femtosecond all-fiber laser provided in an embodiment of the present invention. Figure 4 This is a graph showing the test results of the mode-locked laser output pulse width of the dispersion-managed femtosecond all-fiber laser with adjustable pulse width provided in an embodiment of the present invention. Figure 5 This is a graph showing the test results of the laser output pulse width of the dispersion-managed, pulse-width-adjustable femtosecond all-fiber laser provided in an embodiment of the present invention. Figure 6 This is a graph showing the repetition rate test results of the mode-locked laser output of the dispersion-managed, pulse-width-adjustable femtosecond all-fiber laser provided by the embodiment of the present invention. Figure 3 , Figure 4 and Figure 5 As shown in the figure, the above laser structure achieves a wide spectrum mode-locked output with a 3dB spectrum width of 17.78nm, and its pulse compression limit is 80fs; by adjusting the dispersion of the second chirped fiber Bragg grating, the output laser pulse width can be tuned in the range of 5.4ps to 688ps; by adjusting the second-order dispersion introduced by the pulse compressor, the output laser pulse width can be tuned in the range of hundreds of femtoseconds to sub-nanoseconds. Figure 6 As shown, the repetition rate is 41.5MHz. Through the selector, the repetition rate range of 1MHz~41.5MHz can be achieved; at a repetition rate of 2MHz, the output power is >2W, and the single pulse energy is >1μJ. When the first pump source power is 70mW, the fiber laser oscillator output power is 12mW. After broadening and selector loss, the output power is 5mW. When the second pump source power is 300mW, the primary prevention maximum output power is 60mW; when the third pump source power is 5W, the final output power is 2W.

[0054] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the protection scope of the technical solution of the present invention.

Claims

1. A dispersion-managed femtosecond all-fiber laser with adjustable pulse width, characterized in that: It includes: A mode-locked light source (27), a pulse laser amplifier (26) and a pulse compressor (28) composed of a fiber laser oscillator (7), a pulse stretcher (10) and a selector (15); The fiber laser oscillator, pulse stretcher, selector and pulse laser amplifier are all connected via optical fibers. The fiber laser oscillator adopts a linear short cavity structure and an extracavity pumping method. The output end of the fiber laser oscillator is connected to the input end of the pulse stretcher. The pulse stretcher includes a fiber circulator (8) and a second chirped fiber Bragg grating (9). The central wavelength of the second chirped fiber Bragg grating is in the range of 1020nm to 1040nm. The output end of the pulse stretcher is connected to the input end of the selector. The selector includes a fiber acousto-optic modulator (11), a light detector (12), a radio frequency driver (13), a pulse selector (14), the output end of the selector is connected to the input end of a pulse laser amplifier, and the pulse laser amplifier includes a first-stage preamplifier (20) and a second-stage main amplifier (25); the fiber laser oscillator generates a wide-spectrum mode-locked pulse laser, the pulse stretcher stretches the pulse width of the laser to the order of hundreds of picoseconds, the laser repetition frequency is tuned by the selector, the laser is power-amplified by the first-stage preamplifier and the second-stage main amplifier, and then enters the pulse compressor to compress the output pulse laser width to the order of femtoseconds; The fiber laser oscillator comprises a semiconductor saturable absorber SESAM (1), a first gain fiber (2), a first chirped fiber Bragg grating (3), a first wavelength division multiplexer (4), a first fiber isolator (5) and a first pump source (6); The first end of the first gain fiber is connected to the semiconductor saturable absorber, and the second end of the first gain fiber is connected to the first end of the first chirped fiber Bragg grating; the second end of the first chirped fiber Bragg grating is connected to the output end of the first wavelength division multiplexer, the output end of the first pump source is connected to the pump input end of the first wavelength division multiplexer, and the input end of the first wavelength division multiplexer is connected to the input end of the first optical fiber isolator.

2. The dispersion-managed femtosecond all-fiber laser with adjustable pulse width according to claim 1, characterized in that: The pigtails of the passive devices in the fiber laser oscillator are all polarization-maintaining fibers, and the dispersion of the polarization-maintaining fibers in the central band of the fiber Bragg grating is positive dispersion; the dispersion of the first gain fiber in the central band of the fiber Bragg grating is positive dispersion.

3. The dispersion-managed femtosecond all-fiber laser with adjustable pulse width according to claim 2, characterized in that: The first wavelength division multiplexer is located outside the laser resonant cavity and couples the pump light output by the pump source into the fiber laser oscillator.

4. The dispersion-managed femtosecond all-fiber laser with adjustable pulse width according to claim 3, characterized in that: Through dispersion management, SESAM and the first chirped fiber Bragg grating are used as cavity mirrors to form a resonant cavity, wherein the first chirped fiber Bragg grating uses temperature control to control the second-order negative dispersion provided to compensate for the second-order positive dispersion brought by the optical fiber in the resonant cavity, so that the net cavity dispersion tends to zero, and the first chirped fiber Bragg grating is partially transmitted as an output coupling mirror.

5. The dispersion-managed femtosecond all-fiber laser with adjustable pulse width according to claim 4, characterized in that: The semiconductor saturable absorber SESAM is packaged in the form of optical fiber.

6. The dispersion-managed femtosecond all-fiber laser with adjustable pulse width according to claim 5, characterized in that: The first-stage pre-amplification part comprises a second wavelength division multiplexer (16), a second gain optical fiber (17), a second pump source (18) and a second optical fiber isolator (19); the input end of the second wavelength division multiplexer is connected to the output end of the optical fiber acousto-optic modulator, the output end of the second pump source is connected to the pump input end of the second wavelength division multiplexer, the output end of the second wavelength division multiplexer is connected to the first end of the second gain optical fiber, the second end of the second gain optical fiber is connected to the input end of the second optical fiber isolator, and the output end of the second optical fiber isolator is connected to the second-stage main amplification part, wherein the pigtails of the passive components of the first-stage pre-amplification part are all polarization-maintaining optical fibers.

7. The dispersion-managed femtosecond all-fiber laser with adjustable pulse width according to claim 6, characterized in that: The secondary main amplification part comprises a beam combiner (21), a third gain optical fiber (22), a third pump source (23) and a third optical fiber isolator (24); the input end of the beam combiner is connected to the output end of the primary prevention part, the output end of the third pump source is connected to the pump input end of the beam combiner, the output end of the beam combiner is connected to the first end of the third gain optical fiber, the second end of the third gain optical fiber is connected to the input end of the third optical fiber isolator, and the output end of the third optical fiber isolator is used to output the amplified pulse laser beam; wherein the third pump source is a multimode pump, and the third gain optical fiber is a double-clad ytterbium-doped gain optical fiber.

8. The dispersion-managed femtosecond all-fiber laser with adjustable pulse width according to claim 7, characterized in that: The high-power multi-mode pump source of the secondary main amplifier part adopts a semiconductor laser with a wavelength of 976nm, and the beam combiner uses the pump light of the high-power multi-mode pump source to pump the third gain optical fiber through cladding pumping.

9. The dispersion-managed femtosecond all-fiber laser with adjustable pulse width according to claim 8, characterized in that: The high-power pulse laser output by the pulse laser amplifier enters the pulse compressor to compress the pulse width of the output pulse laser to the femtosecond level, and tunes the pulse width by adjusting the dispersion amount.

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