Ytterbium-doped fiber mode-locked laser

Abstract

The invention discloses an ytterbium-doped optical fiber mode-locked laser. The ytterbium-doped optical fiber mode-locked laser comprises a first pumping source, a first regenerator, a second pumping source and a second regenerator, wherein the first regenerator comprises a first ytterbium-doped optical fiber and a pulse broadening device, and the second regenerator comprises an isolator, a pulse compression device, a frequency spectrum broadening optical fiber and a band-pass filter; the design of a staggered band-pass filter is realized through two regenerators, spectrum broadening caused by a self-phase modulation effect is realized, and mode-locked pulse output can be realized through energy input of a first pumping source and a second pumping source; the peak power is reduced by broadening the pulse so as to reduce the nonlinear effect, the high-energy output pulse is generated in the optical fiber mode-locked laser, meanwhile, the central wavelength interval between the pulse broadening device and the band-pass filter can effectively prevent noise and continuous component oscillation starting, and the pulse quality is improved.

Description

Technical Field

[0001] The invention relates to the field of mode-locked lasers, and in particular to an ytterbium-doped optical fiber mode-locked laser. Background Art

[0002] As an important branch of modern laser technology, the background technology of ytterbium-doped fiber mode-locked laser integrates the latest achievements of materials science, optical engineering and electronic technology. With its unique gain characteristics, such as wide absorption band, high quantum efficiency and low pumping threshold, ytterbium-doped fiber has become an ideal gain medium for high-power and high-efficiency laser output. Mode-locking technology, as a key technology for achieving ultrashort pulse output, can highly compress laser pulses in time by precisely controlling the phase relationship of each longitudinal mode in the laser cavity, thereby outputting lasers with high peak power and narrow pulse width.

[0003] However, in the development of high-power ytterbium-doped fiber mode-locked lasers, the suppression of nonlinear effects has become a key issue that needs to be solved urgently. Nonlinear effects, such as self-phase modulation, four-wave mixing, and soliton effects, will introduce additional phase changes and energy losses during laser transmission, leading to laser pulse distortion, spectrum broadening, and output power reduction. These nonlinear effects are particularly significant under conditions of high power density and long fiber length, which seriously limits the output efficiency of the laser. Summary of the invention

[0004] In view of this, in order to solve one of the above problems, the present invention provides an ytterbium-doped fiber mode-locked laser, which reduces the peak power by broadening the pulse to alleviate the nonlinear effect, thereby generating high-energy output pulses in the fiber mode-locked laser.

[0005] The present invention provides an ytterbium-doped fiber mode-locked laser, comprising a first pump source, a first regenerator, a second pump source and a second regenerator; wherein:

[0006] The first regenerator is connected end to end with the second regenerator; the first pump source provides energy for the first regenerator; and the second pump source provides energy for the second regenerator.

[0007] The first regenerator includes a first ytterbium-doped optical fiber and a pulse stretching device; the second regenerator includes an isolator, a bandpass filter, a pulse compression device and a spectrum stretching optical fiber; the central wavelength of the pulse stretching device is spaced apart from the central wavelength of the bandpass filter; the passband of the pulse stretching device is spaced apart from the passband of the bandpass filter.

[0008] The pulse stretching device comprises a first chirped volume Bragg grating; the pulse compression device comprises a second chirped volume Bragg grating.

[0009] The first regenerator and the second regenerator are both used for bandpass filtering and generating spectrum broadening caused by self-phase modulation effect.

[0010] The present invention provides an ytterbium-doped fiber mode-locked laser, comprising a first pump source, a first regenerator, a second pump source and a second regenerator. The first regenerator comprises a first ytterbium-doped fiber and a pulse stretching device, the second regenerator comprises an isolator, a bandpass filter, a pulse compression device and a spectrum stretching fiber, the pulses in both the first regenerator and the second regenerator generate spectrum broadening caused by the self-phase modulation effect; the pulse stretching device and the central wavelength of the bandpass filter are spaced apart, and the bandpasses are also different; therefore, the two regenerators can realize the design of a dislocated bandpass filter, and have spectrum broadening caused by the self-phase modulation effect, and the energy input of the first pump source and the second pump source can realize mode-locked pulse output; the present invention reduces the peak power by stretching the pulse to alleviate the nonlinear effect, and realizes the generation of high-energy output pulses in the fiber mode-locked laser, and at the same time, the center wavelength interval between the pulse stretching device and the bandpass filter can effectively prevent the oscillation of noise and continuous components, and improve the pulse quality.

[0011] Furthermore, the first regenerator also includes a first optical fiber combiner and an optical fiber coupler.

[0012] The first fiber combiner, the first ytterbium-doped fiber, the fiber coupler and the pulse stretching device are connected in sequence.

[0013] The pulse stretching device performs normal dispersion stretching on the incoming pulse, and then the pulse enters the second ytterbium-doped optical fiber for amplification; the pulse stretching device has the function of bandpass filtering.

[0014] The spectrum broadening optical fiber is used to make the pulse compressed by the pulse compression device undergo nonlinear spectrum broadening, so that part of the spectrum can pass through the bandpass filter. The amount of nonlinear spectrum broadening is adjusted by the length of the spectrum broadening.

[0015] In it, when the laser works for the first time, the first pump source and the second pump source need to output pump light of a certain power to excite the gain medium in the ytterbium-doped optical fiber. Since the ytterbium-doped optical fiber has good heat dissipation performance, a wide absorption band and stable output, it can be efficiently coupled into the optical fiber, thereby improving the pump efficiency of the laser, effectively coupling the pump light into the optical fiber, and making the laser work stably. The present invention also provides a seed laser, which is connected to the optical fiber coupler to form a seed starting device. After the laser works for the first time, through the staggered bandpass, spectrum broadening and pump input of the two regenerators, after the Mamyshev mechanism is formed, the laser's intracavity parameters such as pump power and filter bandpass frequency band are fixed, and the locking mode can be started by starting the seed pulse injection.

[0016] Furthermore, the pulse stretching device also includes a fiber circulator and a fiber collimator.

[0017] One end of the optical fiber circulator is connected to the optical fiber coupler, and the other end of the optical fiber circulator is connected to the second regenerator.

[0018] Therein, the pulse entering the pulse stretching device enters the free space from the fiber collimator through the fiber circulator, is pulse stretched to a preset standard by the first chirped body Bragg grating, and then is reflected back to the fiber collimator, and finally enters the second fiber combiner and the second ytterbium-doped fiber connected to the fiber circulator from the fiber circulator.

[0019] Furthermore, the pulse passing through the pulse stretching device has the following characteristics:

[0020] Pulse width is within 0.5-5ps;

[0021] The spectral width is between 5-20nm;

[0022] The pulse energy is greater than 100 pJ.

[0023] Optionally, the pulse stretching device can stretch the normal dispersion of the incoming pulse to the order of hundreds of picoseconds to nanoseconds, and adjust the incoming pulse according to preset parameters, and the stretched pulse enters the second ytterbium-doped optical fiber for amplification. The preset parameters include the central wavelength, bandwidth, and dispersion amount.

[0024] Optionally, the optical fiber coupler includes a 2×2 optical fiber coupler; and the splitting ratio of the optical fiber coupler includes 50 / 50.

[0025] Among them, the type and performance parameters of the optical fiber coupler are configured according to the implementation requirements.

[0026] Furthermore, the second regenerator also includes a second beam combiner and a second ytterbium-doped optical fiber.

[0027] The second fiber combiner, the second ytterbium-doped fiber, the isolator, the pulse compression device, the spectrum broadening fiber and the bandpass filter are connected in sequence.

[0028] Specifically, the pulse compression device also includes a wave plate, a first polarization beam splitter cube, a second polarization beam splitter cube, a second fiber collimator and a third fiber collimator; one end of the second fiber collimator is connected to the second ytterbium-doped fiber; one end of the third fiber collimator is connected to the spectrum broadening fiber.

[0029] Optionally, in the pulse compression device, the wave plate includes a first half-wave plate, a second half-wave plate and a quarter-wave plate.

[0030] Specifically, the pulse passing through the second ytterbium-doped optical fiber passes through the second optical fiber collimator, the isolator, the first polarization beam splitter cube, the quarter wave plate, and the second chirped body Bragg grating in sequence, is reflected from the second chirped body Bragg grating back to the first polarization beam splitter cube, and then passes through the first half-wave plate, the second polarization beam splitter cube, the second half-wave plate, and the third optical fiber collimator in sequence, and finally enters the spectrum broadening optical fiber.

[0031] Optionally, the pulse compression device is used to output the compressed laser energy according to a preset ratio.

[0032] Specifically, the pulse compression device compresses the pulse amplified by the second ytterbium-doped optical fiber according to preset parameters, and the preset parameters of the pulse compression device such as the central wavelength, bandwidth and dispersion amount are consistent with those of the stretching device, and anomalous dispersion is introduced, and the compressed laser energy is output according to a preset ratio, and the remaining energy returns to the spectrum stretching optical fiber. Furthermore, the bandpass filter includes a bandpass filter with a bandwidth in the order of nm; the bandwidth of the bandpass filter is smaller than the bandwidth of the pulse stretching device and the bandwidth of the pulse compression device.

[0033] It should be noted that in a mode-locked laser implemented in the present invention, the first regenerator includes a first fiber combiner, a first ytterbium-doped fiber, a fiber coupler, and a pulse stretching device; the second regenerator includes a second fiber combiner, a second ytterbium-doped fiber, a pulse compression device, a spectrum stretching fiber, and a bandpass filter; the first regenerator and the second regenerator are connected to form a ring resonator, and then the central wavelength and passband of the bandpass filter and the pulse stretching device are separated, and the spectrum broadening caused by the staggered bandpass filter setting and the self-phase modulation effect satisfies the Mamyshev mode-locking mechanism, and finally the first pump source and the second pump source provide energy to the resonator to achieve mode-locked pulse output.

[0034] The Mamyshev mechanism refers to a passive mode-locking technology used in mode-locked lasers. The mode-locking technology locks multiple longitudinal mode light waves together so that they overlap in time and interfere to form ultrashort pulses. The characteristic of the Mamyshev mechanism is that mode locking is achieved through the setting of staggered bandpass filters and the spectrum broadening caused by the self-phase modulation effect.

[0035] Specifically, the mode-locked laser implemented in the present invention includes two cascaded regenerators, which generate pulses through spectrum broadening and spectrum filtering. This structure determines that high-peak power pulses can pass through the filter after the spectrum is fully broadened after self-phase modulation, while low-peak power pulses are not fully spectrum broadened and are isolated by the bandpass filter. Cascading this process manifests as a significantly enhanced saturable absorption effect: high-intensity pulses are passed while pulses below a certain intensity are suppressed. Only sufficiently strong pulses can cross the gap between the two filters and enter the next arm.

[0036] The embodiments of the present invention have the following beneficial effects:

[0037] The embodiment of the present invention provides a mode-locked laser, wherein a first regenerator comprises a first fiber combiner, a first ytterbium-doped fiber, a fiber coupler, and a pulse stretching device, and a second regenerator comprises a second fiber combiner, a second ytterbium-doped fiber, a pulse compression device, a spectrum stretching fiber, and a bandpass filter; the pulse generates spectrum broadening caused by the self-phase modulation effect in both the first regenerator and the second regenerator; the pulse stretching device and the central wavelength of the bandpass filter are spaced apart, and the bandpasses are also different; therefore, the two regenerators can realize the design of a staggered bandpass filter, and have spectrum broadening caused by the self-phase modulation effect, and the energy input of the first pump source and the second pump source can realize mode-locked pulse output; the present invention reduces the peak power by stretching the pulse to alleviate the nonlinear effect, and further compresses and outputs the pulse, so as to realize the generation of high-energy output pulses in the fiber mode-locked laser, and at the same time, the center wavelength interval between the pulse stretching device and the bandpass filter can effectively prevent the oscillation of noise and continuous components, thereby improving the pulse quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 1 is a schematic diagram of the structure of an ytterbium-doped fiber mode-locked laser provided in an embodiment of the present invention;

[0039] Figure 2 is a schematic structural diagram of another ytterbium-doped fiber mode-locked laser provided in an embodiment of the present invention;

[0040] Figure 3 is a schematic diagram of a pulse output spectrum of an ytterbium-doped fiber mode-locked laser provided in an embodiment of the present invention;

[0041] Figure 4 is a schematic diagram of an autocorrelation measurement result of a pulse output of an ytterbium-doped fiber mode-locked laser provided in an embodiment of the present invention;

[0042] Figure 2Figure numerals: first pump source 1, first fiber combiner 2, first ytterbium-doped fiber 3, seed laser 4, fiber coupler 5, fiber circulator 6, first fiber collimator 7, first chirped volume Bragg grating 8, second pump source 9, second fiber combiner 10, second ytterbium-doped fiber 11, second fiber collimator 12, isolator 13, first polarization splitter cube 14, quarter wave plate 15, first half-wave plate 16, second polarization splitter cube 17, second half-wave plate 18, third fiber collimator 19, spectrum broadening fiber 20, bandpass filter 21, second chirped volume Bragg grating 22. DETAILED DESCRIPTION

[0043] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The step numbers in the following embodiments are only provided for the convenience of explanation and description, and the order between the steps is not limited in any way. The execution order of each step in the embodiment can be adaptively adjusted according to the understanding of those skilled in the art.

[0044] like Figure 1 As shown, Figure 1 is a schematic diagram of the structure of an ytterbium-doped fiber mode-locked laser provided in an embodiment of the present invention. This embodiment provides an ytterbium-doped fiber mode-locked laser, including a first pump source, a first regenerator, a second pump source and a second regenerator; wherein,

[0045] The first regenerator is connected end to end with the second regenerator; the first pump source provides energy for the first regenerator; and the second pump source provides energy for the second regenerator.

[0046] The first regenerator includes an ytterbium-doped optical fiber and a pulse stretching device; the second regenerator includes an isolator, a pulse compression device, a spectrum stretching optical fiber and a bandpass filter; the central wavelength of the pulse stretching device is spaced apart from the central wavelength of the bandpass filter; the passband of the pulse stretching device is spaced apart from the passband of the bandpass filter.

[0047] The pulse stretching device comprises a first chirped volume Bragg grating; the pulse compression device comprises a second chirped volume Bragg grating;

[0048] The first regenerator and the second regenerator are both used for bandpass filtering and generating spectrum broadening caused by the self-phase modulation effect.

[0049] Specifically, the pulse stretching device performs normal dispersion stretching on the incoming pulse, and then the pulse is output to the second regenerator for amplification. The pulse stretching device also has the function of bandpass filtering.

[0050] Specifically, the spectrum broadening optical fiber is used to make the pulse compressed by the pulse compression device undergo nonlinear spectrum broadening, so that part of the spectrum can pass through the bandpass filter. The amount of nonlinear spectrum broadening is adjusted by the length of the spectrum broadening.

[0051] This embodiment provides an ytterbium-doped fiber mode-locked laser, including a first pump source, a first regenerator, a second pump source, and a second regenerator. The first regenerator includes an ytterbium-doped fiber and a pulse stretching device, and the second regenerator includes an isolator, a pulse compression device, a spectrum stretching fiber, and a bandpass filter. The pulse generates spectrum broadening caused by the self-phase modulation effect in the ytterbium-doped fiber and the spectrum stretching fiber; the pulse stretching device and the center wavelength of the bandpass filter are spaced apart, and the bandpass is also different; therefore, the two regenerators can realize the design of a staggered bandpass filter, and have spectrum broadening caused by the self-phase modulation effect, and the energy input of the first pump source and the second pump source can realize mode-locked pulse output; the present invention reduces the peak power by stretching the pulse to alleviate the nonlinear effect, and realizes the generation of high-energy output pulses in the fiber mode-locked laser, and the center wavelength interval between the pulse stretching device and the bandpass filter can effectively prevent the oscillation of noise and continuous components, thereby improving the pulse quality.

[0052] like Figure 2 As shown, Figure 2 1 is a schematic diagram of the structure of another ytterbium-doped fiber mode-locked laser provided in an embodiment of the present invention. In this embodiment, another ytterbium-doped fiber mode-locked laser is provided, including a first pump source 1, a first fiber combiner 2, a first ytterbium-doped fiber 3, a seed laser 4, a fiber coupler 5, a fiber circulator 6, a first fiber collimator 7, a first chirped volume Bragg grating 8, a second pump source 9, a second fiber combiner 10, a second ytterbium-doped fiber 11, a second fiber collimator 12, an isolator 13, a first polarization splitter cube 14, a quarter wave plate 15, a first half-wave plate 16, a second polarization splitter cube 17, a second half-wave plate 18, a third fiber collimator 19, a spectrum broadening fiber 20, a bandpass filter 21, and a second chirped volume Bragg grating 22.

[0053] Among them, the pulse broadening device includes a fiber circulator 6, a first fiber collimator 7, and a first chirped volume Bragg grating 8; the pulse compression device includes a second fiber collimator 12, an isolator 13, a first polarization beam splitter cube 14, a quarter wave plate 15, a first half wave plate 16, a second polarization beam splitter cube 17, a second half wave plate 18, a third fiber collimator 19, and a second chirped volume Bragg grating 22.

[0054] The first fiber combiner 2, the first ytterbium-doped fiber 3, the fiber coupler 5, the pulse stretching device, the second ytterbium-doped fiber 11, the isolator 13, the pulse compression device, the spectrum stretching fiber 20 and the bandpass filter 21 are sequentially connected by fiber fusion to form a ring resonant cavity. The first pump source 1 and the second pump source 9 provide energy for the ring resonant cavity, and the ring resonant cavity and the first pump source 1 and the second pump source 9 form a mode-locked oscillator; the mode-locked pulse output is achieved through the mode-locked oscillator.

[0055] There is a gap between the central wavelength of the pulse stretching device and the central wavelength of the bandpass filter 21 ; there is a gap between the passband of the pulse stretching device and the passband of the bandpass filter 21 .

[0056] In this embodiment, the first ytterbium-doped optical fiber 3 performs normal dispersion broadening on the incoming pulse, so that the pulse produces spectrum broadening caused by the self-phase modulation effect, and then passes through a pulse broadening device with a bandpass filtering effect.

[0057] Specifically, the spectrum broadening optical fiber 20 causes the pulse compressed by the pulse compression device to generate spectrum broadening caused by the self-phase modulation effect, so that part of the spectrum can pass through the bandpass filter 21. The nonlinear spectrum broadening amount is adjusted by the length of the spectrum broadening optical fiber 20. The spectrum broadening optical fiber used in the embodiment of the present invention is PM10-125 optical fiber with a length of 6m.

[0058] Specifically, when the laser works for the first time, the first pump source 1 and the second pump source 9 need to output pump light of a certain power to excite the gain medium in the ytterbium-doped fiber. Since the ytterbium-doped fiber has good heat dissipation performance, a wide absorption band and stable output, it can be efficiently coupled into the optical fiber, thereby improving the pump efficiency of the laser, so that the pump light is effectively coupled into the optical fiber to make the laser work stably. This embodiment also provides a seed laser 4, which is connected to the fiber coupler 5 to form a seed starting device. After the laser works for the first time, through the pulse stretching device and the staggered bandpass of the bandpass filter, the pulse generates spectral broadening and pump input caused by the self-phase modulation effect in the first ytterbium-doped fiber and the spectrum stretching fiber. After the Mamyshev mechanism is formed, the intracavity parameters such as the laser's pump power and the filter bandpass frequency band are fixed, and the mode locking can be started by starting the seed pulse injection.

[0059] It should be noted that the seed laser 4 used in the implementation of the present invention is a passively mode-locked ytterbium-doped laser, and the central wavelength of the output seed pulse is 1030nm, the bandwidth is 3nm, the pulse energy is 0.2nJ, and the repetition frequency is 27.7MHz.

[0060] The chirped volume Bragg grating used in the embodiment of the present invention has a central wavelength of 1030nm, a bandwidth of 7.8nm, and a dispersion coefficient of 50ps / nm; one end of the fiber circulator is connected to the fiber coupler 5, and the other end of the fiber circulator is connected to the second fiber combiner 10.

[0061] Therein, the pulse entering the pulse stretching device enters the free space from the first fiber collimator through the fiber circulator, is pulse stretched to a preset standard by the first chirped body Bragg grating, and then is reflected back to the fiber collimator, and finally enters the second fiber combiner 10 and the second ytterbium-doped fiber 11 connected to the fiber circulator from the fiber circulator.

[0062] Furthermore, the pulse passing through the pulse stretching device 6 has the following characteristics:

[0063] Pulse width is within 0.5-5ps;

[0064] The spectral width is between 5-20nm;

[0065] The pulse energy is greater than 100 pJ.

[0066] Specifically, the pulse stretching device performs normal dispersion stretching on the incoming pulse to the order of hundreds of picoseconds to nanoseconds, and adjusts the incoming pulse according to preset parameters, and the stretched pulse enters the second ytterbium-doped optical fiber for amplification. The preset parameters include the central wavelength, bandwidth, and dispersion amount.

[0067] Optionally, the optical fiber coupler 5 includes a 2×2 optical fiber coupler; and the optical fiber coupler 5 has a splitting ratio of 50 / 50.

[0068] Among them, the type and performance parameters of the optical fiber coupler are configured according to the implementation requirements.

[0069] Furthermore, the pulse compression device includes a first half-wave plate 16 , a second half-wave plate 18 , a quarter-wave plate 15 , a first polarization beam splitter cube 14 , a second polarization beam splitter cube 17 , a second fiber collimator 12 and a third fiber collimator 19 .

[0070] Specifically, the pulse passing through the second ytterbium-doped optical fiber passes through the second optical fiber collimator, the isolator, the first polarization beam splitter cube, the quarter wave plate, and the second chirped body Bragg grating in sequence, is reflected from the second chirped body Bragg grating back to the first polarization beam splitter cube, and then passes through the first half-wave plate, the second polarization beam splitter cube, the second half-wave plate, and the third optical fiber collimator in sequence, and finally enters the spectrum broadening optical fiber.

[0071] Optionally, the pulse compression device is used to output the compressed laser energy according to a preset ratio (optionally >80%).

[0072] Specifically, the pulse compression device compresses the pulse amplified by the second ytterbium-doped optical fiber 11 according to preset parameters. The preset parameters of the pulse compression device, such as the central wavelength, bandwidth and dispersion amount, are consistent with those of the broadening device. Anomalous dispersion is introduced, and the compressed laser energy is output according to a preset ratio, and the remaining energy returns to the spectrum broadening optical fiber 12.

[0073] Furthermore, the bandpass filter includes a bandpass filter with a bandwidth in the order of nm; the bandwidth of the bandpass filter is smaller than the bandwidth of the pulse stretching device and the bandwidth of the pulse compression device.

[0074] In this embodiment, the central wavelength of the bandpass filter 20 is adjustable in the range of 1030-1040. The bandwidth of the bandpass filter 20 used in the embodiment of the present invention is 2.8nm, and the central wavelength is adjustable in the range of 1030-1040nm. The first pump source 1 outputs pump light and is incident on the mode-locked oscillator through the first fiber combiner 2; the second pump source 9 outputs pump light and is incident on the mode-locked oscillator through the second fiber combiner 10; the first pump source 1 and the second pump source 9 output pump light in the 980nm band.

[0075] In this embodiment, the first pump source 1 and the second pump source 9 output pump light of 976nm, the maximum pump power is 9W and 18W respectively, the output fiber is a 105 / 125 multimode fiber, and is respectively incident through the 105 / 125 end of the first fiber combiner 2 and the second fiber combiner 10. The first ytterbium-doped fiber 3 is a Nufern PLMA-YDF-10 / 125-M fiber with a length of 3.4m; the second ytterbium-doped fiber 11 is a Nufern PLMA-YDF-14 / 125-UF fiber with a length of 1.5m.

[0076] In this embodiment, the operating wavelengths of other unexplained components are all 1030 nm, and the pigtails are all PM10-125.

[0077] It should be noted that a mode-locked laser implemented in the present invention includes a ring resonator composed of a first fiber combiner 2, a first ytterbium-doped fiber 3, a fiber coupler 5, a pulse stretching device, a second fiber combiner 10, a second ytterbium-doped fiber 11, a pulse compression device, a spectrum stretching fiber 20 and a bandpass filter 21 connected in sequence, and then the central wavelength and passband of the bandpass filter 21 and the pulse stretching device are separated, and the spectrum broadening caused by the staggered bandpass filter setting and the self-phase modulation effect satisfies the Mamyshev mode-locking mechanism, and finally the first pump source and the second pump source provide energy to the resonator to realize mode-locked pulse output.

[0078] like Figure 3 ,4 As shown, Figure 3 is a schematic diagram of a pulse output spectrum of an ytterbium-doped fiber mode-locked laser provided in an embodiment of the present invention, Figure 4 Schematic diagram of the autocorrelation measurement result of the pulse output of an ytterbium-doped fiber mode-locked laser provided in an embodiment of the present invention. In this embodiment, a mode-locked pulse output with a maximum energy of 244 nJ can be obtained.

[0079] The Mamyshev mechanism refers to a passive mode-locking technology used in mode-locked lasers. The mode-locking technology locks multiple longitudinal mode light waves together so that they overlap in time and interfere to form ultrashort pulses. The characteristic of the Mamyshev mechanism is that mode locking is achieved through the setting of staggered bandpass filters and the spectrum broadening caused by the self-phase modulation effect.

[0080] Specifically, in the mode-locked laser implemented in the present invention, pulses are generated by spectrum broadening and spectrum filtering. This structure determines that high-peak power pulses can pass through the filter after the spectrum is fully broadened after self-phase modulation, while low-peak power pulses are not fully spectrum broadened and are isolated by the bandpass filter. Cascading this process manifests as a significantly enhanced saturable absorption effect: high-intensity pulses are passed while pulses below a certain intensity are suppressed, and only sufficiently strong pulses can cross the interval between the two filters and enter the next arm.

[0081] In summary, the implementation of the embodiments of the present invention has the following beneficial effects:

[0082] The present embodiment provides a mode-locked laser, comprising a first fiber combiner 2, a first ytterbium-doped fiber 3, a fiber coupler 5, a pulse stretching device, a second fiber combiner 10, a second ytterbium-doped fiber 11, a pulse compression device, a spectrum stretching fiber 20 and a bandpass filter 21; the pulse stretching device and the bandpass filter have a central wavelength interval and different bandpasses; therefore, the pulse stretching device and the bandpass filter 21 can realize the design of a staggered bandpass filter, and at the same time, the pulse can generate spectrum broadening caused by the self-phase modulation effect in the first ytterbium-doped fiber and the spectrum stretching fiber 12, and the energy input of the first pump source and the second pump source can realize mode-locked pulse output; the present invention reduces the peak power by stretching the pulse to alleviate the nonlinear effect, and further compresses and outputs the pulse, so as to realize the generation of high-energy output pulses in the fiber mode-locked laser, and at the same time, the central wavelength interval between the pulse stretching device and the bandpass filter can effectively prevent the oscillation of noise and continuous components, thereby improving the pulse quality.

[0083] It can be seen that the contents of the above method embodiments are all applicable to the present system embodiments, the functions specifically implemented by the present system embodiments are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above method embodiments.

[0084] The above is a specific description of the preferred implementation of the present invention, but the invention is not limited to the embodiments. Those skilled in the art may make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. An ytterbium-doped fiber mode-locked laser, characterized in that: It includes a first pump source, a first regenerator, a second pump source and a second regenerator; wherein, The first regenerator is connected end to end with the second regenerator; the first pump source provides energy for the first regenerator; the second pump source provides energy for the second regenerator; The first regenerator comprises a first ytterbium-doped optical fiber and a pulse stretching device; the second regenerator comprises a bandpass filter, a pulse compression device and a spectrum stretching optical fiber; the central wavelength of the pulse stretching device is spaced from the central wavelength of the bandpass filter; the passband of the pulse stretching device is spaced from the passband of the bandpass filter; The pulse stretching device comprises a first chirped volume Bragg grating; the pulse compression device comprises an isolator and a second chirped volume Bragg grating; The first regenerator and the second regenerator are both used for bandpass filtering and generating spectrum broadening caused by self-phase modulation effect.

2. The ytterbium-doped fiber mode-locked laser according to claim 1, characterized in that: The first regenerator also includes a first optical fiber combiner and an optical fiber coupler; The first fiber combiner, the first ytterbium-doped fiber, the fiber coupler and the pulse stretching device are connected in sequence.

3. The ytterbium-doped fiber mode-locked laser according to claim 2, characterized in that: The pulse stretching device comprises a fiber circulator, a first fiber collimator and a first chirped volume Bragg grating; wherein, One end of the optical fiber circulator is connected to the optical fiber coupler, and the other end of the optical fiber circulator is connected to the second regenerator.

4. An ytterbium-doped fiber mode-locked laser according to any one of claims 1 to 3, characterized in that: The pulses passing through the pulse stretching device have the following characteristics: Pulse width is within 0.5-5ps; The spectral width is between 5-20nm; The pulse energy is greater than 100 pJ.

5. The ytterbium-doped fiber mode-locked laser according to claim 2, characterized in that: The optical fiber coupler includes a 2×2 optical fiber coupler; and the optical splitting ratio of the optical fiber coupler includes 50 / 50.

6. The ytterbium-doped fiber mode-locked laser according to claim 3, characterized in that: The second regenerator also includes a second beam combiner and a second ytterbium-doped optical fiber; The second fiber combiner, the second ytterbium-doped fiber, the isolator, the pulse compression device, the spectrum broadening fiber and the bandpass filter are connected in sequence.

7. The ytterbium-doped fiber mode-locked laser according to claim 6, characterized in that: The pulse compression device also includes a wave plate, a first polarization beam splitter cube, a second polarization beam splitter cube, a second fiber collimator, and a third fiber collimator; one end of the second fiber collimator is connected to the second ytterbium-doped fiber; one end of the third fiber collimator is connected to the spectrum broadening fiber.

8. The ytterbium-doped fiber mode-locked laser according to claim 7, characterized in that: The wave plates include half-wave plates and quarter-wave plates.

9. The ytterbium-doped fiber mode-locked laser according to claim 6, characterized in that: The pulse compression device is used to output the compressed laser energy according to a preset ratio.

10. The ytterbium-doped fiber mode-locked laser according to claim 6, characterized in that: The bandpass filter includes a bandpass filter with a bandwidth in the order of nm; the bandwidth of the bandpass filter is smaller than the bandwidth of the pulse stretching device and the bandwidth of the pulse compression device.

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