1030 nanosecond soliton-like pulse f-p cavity fiber oscillator

Abstract

This invention discloses a 1030 nm soliton-type pulsed F-P cavity femtosecond fiber oscillator, comprising: a mode-locked oscillator cavity, a pump source, a moving mechanism, and a seed source control module; the mode-locked oscillator cavity includes a chirped fiber Bragg grating, a ytterbium-doped fiber, a wavelength division multiplexing (WDM) synthesizer, a beam splitter, and a semiconductor saturable absorber (SESAM); the pump source is connected to the pump port of the WDM synthesizer, the signal port of the WDM synthesizer is connected to the ytterbium-doped fiber and the first end of the beam splitter respectively, and the ytterbium-doped fiber is connected to the chirped fiber Bragg grating; the second end of the beam splitter is connected to the semiconductor saturable absorber (SESAM); by changing the optical path layout of each device in the oscillator, the pump light coupling direction is reversed to avoid interference of the pump light to the SESAM; the mode-locked feedback signal is analyzed in real time by an FPGA, and the pump current adjustment and SESAM switching action are dynamically coordinated to ensure the power stability of the pump source and the synergistic optimization of the SESAM operating point, so that the seed source is in the optimal mode-locked state during long-term operation.

Description

Technical Field

[0001] This invention relates to the field of laser equipment technology, and in particular to a 1030 nm soliton-type pulsed FP cavity femtosecond fiber optic oscillator. Background Technology

[0002] Ultrashort pulse lasers are being increasingly widely used in scientific research, industrial processing, and medical fields. Among these applications, femtosecond-level laser pulse technology is increasingly being incorporated into these fields. Considering its maturity, the term "femtosecond" here refers to the range of tens to hundreds of femtoseconds. Of all femtosecond lasers, mode-locked lasers using Ti:sapphire as the gain material and chirped amplification techniques can produce pulses with high energy and pulse widths of less than tens of femtoseconds. In terms of performance, these lasers are undoubtedly among the most widely used ultrashort pulse lasers. However, as solid-state lasers operating in free space, they are subject to certain limitations in application. Fiber-based ultrashort pulse lasers are more convenient and reliable in application, and come in various types, thus their development has received particular attention.

[0003] High-energy fiber-type femtosecond lasers typically employ chirped pulse amplification techniques. The oscillator (also called the seed source) is the module that generates the femtosecond pulse signal in this amplification process. The most significant performance difference between femtosecond and picosecond pulse signals is that the former requires a sufficiently wide spectrum, while the latter has a very narrow spectrum. When the pulse signal is output from the seed source, its pulse width is already widened due to chirping, typically around 1 nanosecond or wider. However, its pulse width can be compressed to near the Fourier transform limit (below 500 femtoseconds).

[0004] Currently, in 1030 nm soliton-pulsed FP-cavity femtosecond fiber oscillators, the spectral range of the pulses is very wide, and dispersion has a significant impact on the pulses. However, it is difficult to easily and precisely control the dispersion in current 1030 nm soliton-pulsed FP-cavity femtosecond fiber oscillators, and the SESAM device in these oscillators has a relatively short operating lifetime. Summary of the Invention

[0005] In view of this, in order to solve the above-mentioned technical problems, the present invention provides a 1030 nm soliton-type pulsed FP cavity femtosecond fiber optic oscillator.

[0006] The first aspect of the present invention provides a 1030 nm soliton-type pulsed FP cavity femtosecond fiber oscillator, comprising: a mode-locked oscillator cavity, a pump source, a moving mechanism, and a seed source control module; the mode-locked oscillator cavity comprises a chirped fiber Bragg grating, a ytterbium-doped fiber, a wavelength division multiplexing synthesizer, a beam splitter, and a semiconductor saturable absorber (SESAM);

[0007] The pump source is connected to the pump port of the wavelength division multiplexing (WDM) combiner, the signal port of the WDM combiner is connected to the ytterbium-doped fiber and the first end of the beam splitter, the ytterbium-doped fiber is connected to the chirped fiber Bragg grating, and the second end of the beam splitter is connected to the semiconductor saturable absorber (SESAM).

[0008] The pump light emitted from the pump source is coupled into the ytterbium-doped fiber via the wavelength division multiplexing (WDM) combiner. After being amplified by the ytterbium-doped fiber, it forms a gain pulse light. The gain pulse light is then pulse-corrected by the chirped fiber Bragg grating and reflected back into the ytterbium-doped fiber for further gain amplification. The further amplified pulse light passes through the WDM combiner and enters the beam splitter. The beam splitter outputs a portion of the pulse light as a seed source laser output, while the other portion of the pulse light is transmitted to the semiconductor saturable absorber (SESAM) for pulse modulation and reflected back into the mode-locked oscillator cavity to form a soliton pulse.

[0009] The seed source control module has a built-in FPGA chip. The seed source control module is used to analyze the mode-locked feedback signal of the semiconductor saturable absorber (SESAM), and generate a pump source current adjustment command and a SESAM switching control command based on the mode-locked feedback signal. It is also used to send the pump source current adjustment command to the pump source to adjust the output power of the pump source; and to send the SESAM switching control command to the moving mechanism to drive the moving mechanism to perform a switching operation on the operating point of the semiconductor saturable absorber (SESAM).

[0010] In one embodiment, the aforementioned 1030 nm soliton pulsed FP cavity femtosecond fiber oscillator further includes: a first isolator; the two ends of the first isolator are respectively connected to the beam splitter and a first output port, the first output port being used to output seed source laser.

[0011] In one embodiment, the aforementioned 1030 nm soliton-type pulsed FP-cavity femtosecond fiber oscillator further includes: a pump drive assembly; the pump drive assembly includes a pump drive module, a signal detector, a second isolator, and a second output port; the two ends of the second isolator are respectively connected to the beam splitter and the second output port, the second output port is connected to the signal detector, the signal detector is connected to the seed source control module, the seed source control module is connected to the pump drive module, and the pump drive module is connected to the pump source; the signal detector is used to collect the mode-locked feedback signal of the semiconductor saturable absorber (SESAM), the seed source control module is used to generate a pump source current adjustment command based on the mode-locked feedback signal collected by the signal detector and send it to the pump drive module, the pump source current adjustment command is configured after the pump drive module, and adjusts the current output by the pump drive module to the pump source.

[0012] In one embodiment, the aforementioned 1030 nm soliton-type pulsed FP cavity femtosecond fiber oscillator further includes: a third isolator and a third output port; the two ends of the third isolator are respectively connected to the chirped fiber Bragg grating and the third output port.

[0013] In one embodiment, the chirped fiber Bragg grating has an anomalous dispersion value of 0.58 picoseconds / nanometer and a spectral bandwidth of 6 to 15 nanometers.

[0014] In one embodiment, the saturation energy density of the semiconductor saturable absorber (SESAM) is 50 μJ / cm². 2 ~100 uJ / cm 2 .

[0015] In one embodiment, the aforementioned 1030 nm soliton pulsed FP cavity femtosecond fiber oscillator further includes: a beam focuser; the beam focuser is disposed between the semiconductor saturable absorber (SESAM) and the beam splitter, and is used to focus the light beam incident on the surface of the semiconductor saturable absorber (SESAM) to a predetermined spot size range.

[0016] In one embodiment, the wavelength division combiner is a polarization-maintaining wavelength division combiner.

[0017] In one embodiment, the moving mechanism includes a SESAM base, a one-dimensional moving platform, a stepper motor, and a position sensor;

[0018] The semiconductor saturable absorber (SESAM) is fixedly mounted on the SESAM base. The SESAM base is fixedly connected to the one-dimensional moving platform by bolts. The relative angle between the SESAM base and the one-dimensional moving platform is defined by the bolts.

[0019] The output shaft of the stepper motor is coaxially connected to the guide rail shaft of the one-dimensional moving platform. The control terminal of the stepper motor is electrically connected to the seed source control module. The seed source control module is used to send the SESAM point switching control command to the stepper motor. The SESAM point switching control command is configured after the stepper motor to control the stepper motor to drive the one-dimensional moving platform to move along the guide rail.

[0020] The position sensor is installed on the one-dimensional moving platform and is used to collect real-time displacement data of the one-dimensional moving platform.

[0021] In one embodiment, the relative angle between the SESAM base and the one-dimensional moving platform is obtained by collimating the relative displacement direction of the incident light beam focused on the surface of the SESAM under a preset optimal mode-locked state.

[0022] As can be seen from the above technical solutions, this invention completely avoids the interference of pump light on the SESAM by changing the optical path layout of each device within the femtosecond fiber oscillator and reversing the pump light coupling direction. This allows the pump light to couple into the cavity between the ytterbium-doped fiber 30 and the SESAM, and then propagate towards the chirped fiber Bragg grating 20. This layout adjustment does not change the cavity dispersion management strategy and nonlinear compensation mechanism; it only optimizes the energy flow path, enabling the system to maintain stable femtosecond pulse output while significantly improving mode-locking robustness and engineering adaptability. Furthermore, this application uses FPGA to analyze the mode-locking feedback signal in real time and dynamically coordinates pump current adjustment and SESAM switching actions to ensure the power stability of the pump source and the synergistic optimization of the SESAM operating point. This ensures the seed source remains in the optimal mode-locking state during long-term operation, improves the lifespan and long-term stability of the SESAM device, and avoids degradation of saturated absorption characteristics caused by localized ablation. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the structure of a 1030 nm soliton-type pulsed FP cavity femtosecond fiber optic oscillator provided in an embodiment of the present invention;

[0025] Figure 2 This is a schematic diagram of current changes under the conventional current driving method of seed source pumped laser;

[0026] Figure 3 A schematic diagram of pump current changes during "overshoot" mode-locked startup;

[0027] Figure 4 This is a schematic diagram of the structure of a one-dimensional mobile platform provided in an embodiment of the present invention;

[0028] Figure 5 This is a schematic diagram of the structure of the SESAM base provided in an embodiment of the present invention;

[0029] Figure 6 This is a schematic diagram of the optical path and mechanical layout for optical collimation adjustment provided in an embodiment of the present invention.

[0030] Figure description: Pump source 10, pump drive module 11, seed source control module 12, signal detector 13, chirped fiber Bragg grating 20, third isolator 21, third output port 22, ytterbium-doped fiber 30, wavelength division multiplexing synthesizer 40, beam splitter 50, first isolator 51, first output port 52, second isolator 53, second output port 54, semiconductor saturable absorber (SESAM) 60, moving mechanism 70, tension screw 71, push screw 72, screw hole 73. Detailed Implementation

[0031] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] In the description of the embodiments of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application. In addition, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0033] In the description of the embodiments of this application, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a replaceable connection, or an integral connection; they can refer to a mechanical connection or an indirect connection through an intermediate medium; or they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application based on the specific circumstances.

[0034] like Figure 1 As shown, this application provides a 1030 nm soliton-type pulsed FP cavity femtosecond fiber oscillator, including: a mode-locked oscillator cavity, a pump source 10, a moving mechanism 70, and a seed source control module 12; the mode-locked oscillator cavity includes a chirped fiber Bragg grating 20, a ytterbium-doped fiber 30, a wavelength division multiplexing synthesizer 40, a beam splitter 50, and a semiconductor saturable absorber SESAM 60;

[0035] The mode-locked oscillator is a linear cavity structure, also known as a Fabry-Perot type cavity. The mirror function of the mode-locked oscillator is undertaken by the mirror in the semiconductor saturable absorber SESAM60 and the chirped fiber Bragg grating 20 (CFBG).

[0036] Pump source 10 is connected to the pump port of wavelength division combiner 40, and the signal port of wavelength division combiner 40 is connected to the first end of ytterbium-doped fiber 30 and beam splitter 50 respectively. Ytterbium-doped fiber 30 is connected to chirped fiber Bragg grating 20; the second end of beam splitter 50 is connected to semiconductor saturable absorber SESAM 60.

[0037] In this application, the beam splitter 50 employs a 2x2 thin-film beam splitter device with a polarizer incorporated to block light polarized along the fast axis. This ensures that only signals polarized along the slow axis of the fiber can form stable oscillations within the cavity. The splitting ratio of the beam splitter 50 significantly affects both the output of the mode-locked pulse and the initiation of mode-locking. These two factors are conflicting and require a compromise. In this application, a ratio of 80% / 20% to 90% / 10% is selected to ensure good self-initiating mode-locking performance of the seed source.

[0038] The pump light emitted from pump source 10 is coupled into ytterbium-doped fiber 30 via wavelength division multiplexing (WDM) combiner 40. After gain amplification by ytterbium-doped fiber 30, it forms a gain-enhanced pulse light. The gain-enhanced pulse light is pulse-corrected by chirped fiber Bragg grating 20 and then reflected back into ytterbium-doped fiber 30 for further gain amplification. The pulse light after further gain amplification passes through WDM combiner 40 and enters beam splitter 50. Beam splitter 50 outputs a portion of the pulse light as seed source laser output, and the other portion of the pulse light is transmitted to semiconductor saturable absorber SESAM 60 for pulse modulation and reflected back into mode-locked oscillator cavity to form soliton pulses.

[0039] The seed source control module 12 has a built-in FPGA chip. The seed source control module 12 is used to analyze the mode-locked feedback signal of the semiconductor saturable absorber SESAM60, and generate pump source current adjustment command and SESAM switching control command based on the mode-locked feedback signal. It is also used to send the pump source current adjustment command to the pump source 10 to adjust the output power of the pump source 10; and to send the SESAM switching control command to the moving mechanism 70 to drive the moving mechanism 70 to perform a switching operation on the operating point of the semiconductor saturable absorber SESAM60.

[0040] The FPGA chip is a programmable chip that, through user-defined and implanted logic programs, analyzes the mode-lock feedback signal reflected back into the cavity by the semiconductor saturated absorber (SESAM60) monitored by the redundant monitoring ports. This allows for real-time analysis of the mode-lock feedback signal and determination of the stability of the mode-lock state. Because the FPGA chip is programmable, it can dynamically adjust the pump current and the SESAM operating point according to pre-implanted logic algorithms. This enables automatic adjustment and control of the mode-lock function, reducing the mode-lock failure rate and extending the SESAM's lifespan. This approach is more flexible and adaptable than static logic operation.

[0041] It should be noted that the working process of the 1030 nm soliton-type pulsed FP cavity femtosecond fiber optic oscillator provided in this application embodiment is as follows:

[0042] The pump light emitted from pump source 10 couples at the node between ytterbium-doped fiber 30 and semiconductor saturable absorber SESAM 60 into the mode-locked oscillator cavity, propagating only in the direction towards the chirped fiber Bragg grating 20 (CFBG), completely avoiding leakage towards the SESAM. After entering the ytterbium-doped fiber 30, the pump light provides energy to the pulse light in the cavity and amplifies it. The amplified pulse light continues to propagate to the CFBG, where the CFBG corrects the pulse broadened by dispersion and reflects it back into the cavity. The reflected pulse light passes through the ytterbium-doped fiber 30 again to gain energy. Subsequently, after passing through wavelength division multiplexing synthesizer 40 and beam splitter 50, it is split into two paths. One path is output as a seed source, and the other path is incident on the SESAM surface to complete nonlinear modulation, maintaining a stable femtosecond pulse shape. The shaped pulse light returns to the coupling node between the ytterbium-doped fiber 30 and the SESAM, merges with the newly coupled pump light, and propagates again towards the CFBG. Thus, the propagation continues between the SESAM and the CFBG. A stable cycle is formed between them, generating soliton pulses of 1030 nanometers.

[0043] For example, a pump laser with a wavelength of 976 nm is coupled into a mode-locked oscillator cavity via a wavelength division multiplexing (WDM) synthesizer 40 and amplified in a ytterbium-doped fiber 30. When the pulse signal propagates into a chirped fiber Bragg grating 20 (CFBG), not only is the pulse energy amplified, but its spectrum and pulse width are also broadened simultaneously. During the reflection process of the CFBG, the pulse signal undergoes two key effects: firstly, spectral filtering, where the bandwidth of the CFBG adjusts and controls the pulse center wavelength and the range of wavelengths that can be broadened; secondly, dispersion compensation, where the anomalous dispersion provided by the CFBG cancels out the normal dispersion accumulated in the fiber. These effects both alter and stabilize the pulse width; however, the pulse energy is significantly reduced during this process. The returned signal is amplified again in the ytterbium-doped fiber 30, bringing the various dispersions experienced by the pulse closer to an optimal equilibrium state. A small portion of the pulse signal is output from the mode-locked oscillator cavity via a beam splitter 50, while the remaining signal continues to propagate to a semiconductor saturable absorber mirror (SESAM) for pulse compression. During reflection and compression, the pulse energy also decays. Subsequently, the pulse begins the evolution of the next cycle. When the mode-locked oscillation within the mode-locked cavity reaches equilibrium, the pulse signal remains stable at various positions within the cavity. However, because the main components affecting pulse characteristics in the mode-locked oscillation cavity have different effects on the pulse, the results vary. Gain fibers produce non-pure phase shifts, causing pulse spectral broadening; CFBG limits the spectral width and compresses the pulse width through spectral filtering; non-gain fibers increase the pulse width; and SESAM can similarly narrow the pulse width, thus causing differences in the pulse state (pulse width and pulse spectral characteristics) at different positions within the cavity.

[0044] In existing femtosecond oscillators, when the pump light propagates from outside the cavity through the CFBG device to the ytterbium-doped fiber 30, a polarization-maintaining pump source with high polarization is required as the seed source. Otherwise, the mode-locked oscillation of the seed source may be unstable, and in severe cases, mode-locking may not be achieved. This is because unexhausted pump light will continue to propagate to the saturable absorber SESAM, which responds to the pump light. If the pump light reaching its surface is constant, its effect is only to add a stable noise signal, with little impact on saturable absorption. However, if the noise fluctuates significantly, the mode-locking state may be disturbed, affecting the mode-locking of the seed source. Based on this analysis, the embodiments of this application reverse the direction of the pump light, so that the pump light couples between the ytterbium-doped fiber 30 and the SESAM into the cavity and propagates towards the CFBG. This prevents the pump light from leaking towards the SESAM. Furthermore, since there is theoretically no pump light leaking towards the SESAM, the polarization state of the pump light will not directly affect mode-locking. Therefore, ordinary pump lasers can be used, thus reducing hardware costs.

[0045] Simultaneously, the seed source control module 12 utilizes its built-in FPGA chip (with a pre-edited logic program embedded in it) to analyze the mode-locking feedback signal of the semiconductor saturable absorber SESAM60 (this mode-locking feedback signal is output from the idle redundant monitoring port of the beam splitter 50), generating a pump source current adjustment command and a SESAM switching control command. The pump source current adjustment command is sent to the pump source 10 to adjust the output power of the pump source 10. Thus, the control program processes and judges the mode-locking feedback signal, and then adjusts the current of the pump source 10 according to the negative feedback algorithm designed in the program to maintain the stability of the pump output power. The SESAM switching control command is sent to the moving mechanism 70, driving the moving mechanism 70 to perform a switching operation on the working point of the semiconductor saturable absorber SESAM60. Thus, when the mode-locking performance of the currently working area of ​​the SESAM is detected to be deteriorated, the focused beam will be automatically switched to a new working point to restore the mode-locking performance and ensure the working life of the semiconductor saturable absorber SESAM60.

[0046] It should be noted that, in this embodiment, by altering the optical path layout of the devices within the femtosecond fiber oscillator and reversing the pump light coupling direction, the pump light couples between the ytterbium-doped fiber 30 and the SESAM into the cavity and propagates towards the chirped fiber Bragg grating 20, thereby completely avoiding interference from the pump light to the SESAM. This layout adjustment does not change the intracavity dispersion management strategy and nonlinear compensation mechanism; it only optimizes the energy flow path, significantly improving mode-locking robustness and engineering adaptability while maintaining stable femtosecond pulse output. Furthermore, this application uses an FPGA to analyze the mode-locking feedback signal in real time and dynamically coordinates pump current adjustment and SESAM switching actions to ensure the power stability of the pump source and the synergistic optimization of the SESAM operating point. This ensures the seed source remains in the optimal mode-locking state during long-term operation, improves the lifespan and long-term stability of the SESAM device, and avoids degradation of saturated absorption characteristics caused by localized ablation.

[0047] In some embodiments, such as Figure 1 As shown, the aforementioned 1030 nm soliton pulsed FP cavity femtosecond fiber oscillator further includes: a first isolator 51; the two ends of the first isolator 51 are respectively connected to the beam splitter 50 and the first output port 52, and the first output port 52 is used to output seed source laser.

[0048] The first isolator 51 is an isolator that uses polarization-maintaining fiber as the pigtail. Its function is to suppress the interference of backscattered light on the mode-locking process and ensure the temporal stability and polarization purity of the seed source output.

[0049] In some embodiments, such as Figure 1 As shown, the aforementioned 1030nm soliton pulsed FP cavity femtosecond fiber oscillator further includes: a pump drive assembly; the pump drive assembly includes a pump drive module 11, a signal detector 13, a second isolator 53, and a second output port 54; the two ends of the second isolator 53 are respectively connected to the beam splitter 50 and the second output port 54, the second output port 54 is connected to the signal detector 13, the signal detector 13 is connected to the seed source control module 12, the seed source control module 12 is connected to the pump drive module 11, and the pump drive module 11 is connected to the pump source 10; the signal detector 13 is used to collect the mode-locked feedback signal of the semiconductor saturable absorber SESAM60, the seed source control module 12 is used to generate a pump source current adjustment command based on the mode-locked feedback signal collected by the signal detector 13 and send it to the pump drive module 11, the pump source current adjustment command is configured in the pump drive module 11, and the current output by the pump drive module 11 to the pump source 10 is adjusted.

[0050] During the operation of the pump drive component, the pulsed light in the mode-locked oscillator cavity is split by the beam splitter 50, and a portion of the pulsed light is transmitted to the second output port 54 through the second isolator 53. The signal detector 13 collects the pulsed light signal from the second output port 54 and converts it into an electrical signal, which is the mode-locked feedback signal. The electrical signal is then transmitted to the seed source control module 12. The seed source control module 12 analyzes the output state of the pulsed light (such as power, stability, etc.) based on the received mode-locked feedback signal. It judges whether the mode-locked state is stable by the power change of the pulsed light. Generally, when the power fluctuation of the feedback signal exceeds the preset threshold ΔP (typical value is ±3%), it is determined that the mode-locked state has deteriorated. The pump current dynamic compensation mechanism is triggered, and a corresponding control command is generated and sent to the pump drive module 11. After receiving the control command, the pump drive module 11 adjusts the current output to the pump source 10, thereby accurately controlling the pump power of the pump source 10, and finally achieving stable control of the pulsed light output of the entire 1030 nm soliton pulsed FP cavity femtosecond fiber oscillator.

[0051] In the aforementioned seed source control module 12, in addition to the function of starting the pump source 10 to output the pump laser, several important monitoring functions are also extended. At the control level, the connection and interaction between the seed source control module 12 and the optical structure encompasses functions including: starting the pump source 10, controlling the current of the pump source 10, and automatic current adjustment. Furthermore, since the circuit system has a sufficient number of input / output signal ports, the seed source control module 12 can also be expanded with other functions according to programmable chips and application requirements.

[0052] The output power stabilization is achieved through a negative feedback circuit. In the aforementioned pump drive assembly, the circuit's programmed control capability is fully utilized. This power stabilization function is accomplished by the control program processing and judging the feedback signal, and then adjusting the current of the pump source 10 according to the programmed negative feedback algorithm. It can operate not only in the linear region but also in the nonlinear region or other special regions.

[0053] In typical pump sources, the pump laser's current driving method is as follows: Figure 2 As shown, the change of the driving current over time resembles a step. The current jumps from 0 to the stable operating current level and remains there until it is turned off. Of course, the jump actually has a slope, which can be determined by the value of a resistor in the circuit. This startup method requires the seed source to have excellent mode-locking self-starting performance. Otherwise, the seed source cannot meet the requirements of mature products, such as industrial lasers. In the startup behavior of most mode-locked seed sources, it can be observed that, despite the good stability of the optical path and optical components, the mode-locking startup effect always exhibits the following two situations:

[0054] The first scenario is that even a seed source with excellent self-starting performance still has a certain probability of failure. This means that in order to make a seed source truly reliable, in addition to ensuring that the seed source optical path has good mode-locked self-starting performance, a backup plan for mode-locked startup must also be developed so that it can be activated in case of unexpected mode-locked self-starting failure, ensuring that mode-locked startup and normal operation are achieved.

[0055] The second scenario involves a region, sometimes quite large, where mode-locked oscillation self-starting is highly sensitive to the optical path and optical components. Within the selectable range of optical path parameters, the seed source can maintain a stable mode-locked state but cannot achieve self-starting. If manual operation is used, the pump power (actually adjusting the pump current) can be first set above the operating range of single-pulse mode-locking. This initiates mode-locked oscillation, but the mode-locking state is not normal single-pulse mode-locking (e.g., it's in a multi-pulse mode-locking state). Then, the pump power is gradually reduced to the selected single-pulse mode-locking state; this is known as "overshoot" mode-locking initiation. The pump current change during this initiation process is as follows: Figure 3 As shown.

[0056] In this application, after the seed source control module 12 is embedded in a programmable FPGA chip, the aforementioned "overshoot" mode-locking startup technology can be implemented through the logic program edited in the chip, thus achieving automation. Furthermore, the mode-locking feedback signal obtained from the redundant output port (second output port) of the monitoring optical circuit provides the FPGA chip with relevant information about the mode-locking state, enabling the program-controlled mode-locking startup process to determine the mode-locking startup state and make a selection for the next change in current based on the current state. For example, by editing the logic program, if the seed source has entered a certain mode-locking state and can operate stably (such as a multi-pulse mode-locking state) during the current rise process, the FPGA chip program can immediately cause the drive current to begin to decrease until the seed source reaches a stable single-pulse mode-locking operating state.

[0057] In some embodiments, such as Figure 1 As shown, the aforementioned 1030 nm soliton-type pulsed FP cavity femtosecond fiber oscillator also includes: a third isolator 21 and a third output port 22; the two ends of the third isolator 21 are respectively connected to the chirped fiber Bragg grating 20 and the third output port 22.

[0058] Among them, the third isolator 21 can be a single-stage isolator with non-polarization-maintaining fiber as the pigtail. However, the idle fiber end of the third isolator 21 needs to be punched into a small loop that allows the signal to leak from the side of the fiber, so as to maximize the stability of the intracavity mode-locked oscillation.

[0059] In some embodiments, the chirped fiber Bragg grating 20 has an anomalous dispersion value of 0.58 picoseconds / nanometer and a spectral bandwidth of 6 nanometers to 15 nanometers.

[0060] In the design of the mode-locked oscillator, the length of the mode-locked oscillator is essentially the length of the optical fiber inside the cavity. This parameter is related to the required pulse repetition frequency as follows:

[0061]

[0062] In the formula, L is the length of the long fiber inside the cavity; c is the speed of light; n is the refractive index of the optical fiber; and f is the repetition frequency of the pulse.

[0063] The mode-locked oscillator uses polarization-maintaining fiber PM980. Ytterbium-doped fiber 30 is a highly concentrated ytterbium-doped single-mode, single-clad polarization-maintaining fiber. The refractive indices of both can be considered the same, approximately 1.46. Based on this, the fiber length within the oscillator corresponding to various pulse repetition frequencies can be calculated. The dispersion value of the fiber at 1030 nm is approximately 0.044 picoseconds / ( The total normal dispersion of the fiber within the cavity during a single phase can be determined based on the pulse repetition frequency designed for the oscillating cavity. Table 1 lists some typical pulse repetition frequencies, their corresponding fiber lengths within the oscillating cavity, and the total normal dispersion in the 1030 nm band.

[0064] Table 1 Repetition frequency and fiber length in the oscillation cavity

[0065]

[0066] To determine the dispersion parameters of a CFBG, it is first necessary to estimate the sum of the normal dispersion contributed by the fiber in the designed resonant cavity. This value is related to the pulse repetition frequency of the resonant cavity. The third column in Table 1 shows the sum of the normal dispersion of the fiber corresponding to different repetition frequencies. Experiments have shown that, under normal circumstances, for mode-locked oscillation to have sufficiently good mode-locked self-starting performance, the CFBG must provide anomalous dispersion, and the net anomalous dispersion remaining in the cavity after the two dispersions cancel each other out must be above 0.11 picoseconds / nanometer.

[0067] The lowest repetition frequency at which the oscillator can achieve mode-locking self-initiation is 20 MHz, corresponding to a cavity length of 5.14 m and a cumulative normal dispersion of 0.45 picoseconds / nanometer per cycle. Based on this, the anomalous dispersion value of the CFBG is chosen to be 0.58 picoseconds / nanometer. This design is a crucial condition for ensuring good self-initiation mode-locking performance of the seed source at pulse repetition frequencies above 20 MHz. Femtosecond pulses generated within this range exhibit soliton properties. The primary performance objective of our femtosecond oscillator is to achieve good self-initiation mode-locking capability within the selected range.

[0068] In addition, the CFBG also performs an important physical function: "filtering," or controlling and selecting, the spectrum of the pulse. The corresponding parameter is its spectral bandwidth. Similar to the bandwidth selection of the FBG in a picosecond seed source, the spectral bandwidth of the CFBG is related to the spectral characteristics of the generated pulse. Generally, a wider spectral bandwidth makes mode-locking more stable, and the generated pulse can also have a wider spectral width, meaning the pulse can be compressed more narrowly. However, an excessively wide spectral band is detrimental to mode-locked oscillation. In this embodiment, the bandwidth of the CFBG is selected in the range of 6 nanometers to 15 nanometers. Preferably, the bandwidth of the CFBG is selected as 10 nanometers.

[0069] For the ytterbium-doped fiber 30, a highly doped polarization-maintaining single-mode ytterbium fiber is used. The length of the ytterbium-doped fiber 30 used in the mode-locked oscillation cavity has a significant impact on the mode-locking initiation and stable oscillation of the seed source. If the ytterbium-doped fiber 30 is shorter than a certain length (e.g., 20 cm), the mode-locking oscillation becomes unstable. For a mode-locked oscillation cavity that could normally self-initiate, if the gain fiber exceeds a certain length (e.g., 30 cm), the self-initiation of mode-locking of the seed source becomes difficult. However, in this case, after successfully initiating mode-locking, the mode-locking oscillation can usually still proceed stably. Based on these experimental findings, in the design scheme of this application, the ytterbium-doped fiber 30 needs to be controlled between 20 cm and 30 cm. This parameter range is an important design factor for the seed source to achieve good self-initiated mode-locking.

[0070] The main performance parameters affecting mode-locking of a semiconductor saturated absorber mirror (SESAM) include: absorptivity, saturation energy density, modulation depth, relaxation time, and reflection and absorption bandwidth. Among these physical parameters, saturation energy density, modulation depth, and relaxation time have the greatest impact on femtosecond fiber seed sources.

[0071] The following considerations were taken into account when selecting SESAM for the range of these parameters:

[0072] Relaxation Time: The relaxation time of a SESAM also reflects its response speed to a laser pulse. Therefore, for a given mode-locked laser pulse, when the relaxation time of the SESAM is significantly less than the pulse width, its saturated absorption characteristics are related to the instantaneous power of the pulse. In this case, the SESAM is a fast saturated absorber. However, when the relaxation time of the SESAM is significantly greater than the pulse width, its saturated absorption characteristics are mainly affected by the pulse energy and have little to do with the instantaneous power. In this case, the SESAM becomes a "slow" saturated absorber. Both theoretical and experimental results show that using a slow SESAM results in better mode-locking performance for fiber-optic femtosecond oscillators. The actual pulse width of the mode-locked pulse generated by the femtosecond fiber seed source designed in this application is generally less than 1 picosecond, so the relaxation time of the SESAM should be in the range of several picoseconds to tens of picoseconds.

[0073] Modulation depth: Modulation depth indicates the difference in absorption intensity between saturated and unsaturated absorption by a SESAM. Experimental results show that solid-state mode-locked oscillators (SESAMs) with smaller modulation depths are preferable, while fiber-type SESAMs with larger modulation depths are more advantageous. Furthermore, according to general theory of mode-locked lasers, the pulse width of the laser output obtained from mode-locked oscillation is inversely proportional to the modulation depth of the modulator. Therefore, when selecting a SESAM for a fiber-type mode-locked seed source, devices with larger modulation depths should be chosen whenever possible. However, due to practical limitations in device fabrication, the modulation depth of SESAMs rarely exceeds 20%. Therefore, the modulation depth range of the SESAMs selected in the embodiments of this application is generally between 15% and 20%.

[0074] SESAM Saturation Energy Density and Laser Beam Spot Size: Saturation energy density is a parameter related to the threshold pulse energy at which mode-locking can occur within the cavity. Both theoretical and experimental results show that the most stable mode-locking state can be achieved within the resonant cavity when the pulse energy reaches two to five times the saturation energy density of the SESAM. Based on this consideration, the parameter range of the SESAM was analyzed as follows:

[0075] First, it's necessary to roughly determine the pulse energy when the laser beam strikes the SESAM surface. In actual measurements, the average power of the laser beam can usually be directly measured. For a given pulse repetition frequency, a certain average power corresponds to a certain pulse energy. For a seed source of a soliton pulse, the maximum pulse energy of a single pulse within the cavity is limited. On the other hand, for the SESAM to initiate mode-locking, the energy density of the beam reaching the SESAM surface must reach the threshold required for mode-locking. These mode-locking conditions depend not only on the performance parameters of the SESAM device but also on the parameters of other oscillating cavity devices. Among these, the most important and direct device parameters include the coupling ratio of the oscillating cavity output coupler, the position of the coupler within the cavity, and the focusing parameters of the beam focuser associated with the SESAM.

[0076] In the design of this application, to facilitate the formation and initiation of mode-locking within the cavity, the output coupling ratio of the oscillating cavity is selected to be close to the lowest ratio, at 10%:90%, meaning that only 10% of its energy is coupled out after each pulse cycle. Experiments show that this selection makes it easier to initiate mode-locked operation.

[0077] Measurements show that, when this output ratio is selected, the average power of the laser output varies from approximately 0.1 to 0.2 milliwatts when operating within the stable mode-locked range for the mode-locked oscillator with a pulse repetition frequency of approximately 20 MHz designed in this application. Depending on the output coupling ratio, the average power of the laser beam incident on the SESAM surface within the cavity is approximately 1 to 2 milliwatts. Therefore, the pulse energy of the incident pulse is approximately between 50 and 100 picojoules.

[0078] Once the pulse energy within the cavity is determined, the energy density of the beam incident on the SESAM surface is determined by the size of the beam spot on that surface. Assuming the focal spot diameter of the laser beam is D and the pulse energy is E, the pulse energy density Φ can be estimated using the following formula:

[0079]

[0080] If the pulse energy incident on SESAM is around 50 picojoules, then when the beam spot diameter is 4 micrometers, its energy density is approximately 350 uJ / cm². 2 The energy density is approximately 90 uJ / cm² when the beam spot diameter is 8 micrometers. If the incident pulse energy reaches 100 picojoules, the energy density will vary to approximately 180 uJ / cm² within the aforementioned spot size range. 2 Up to 700 uJ / cm 2 Variations within the range.

[0081] In this application, the saturation energy density of the semiconductor saturable absorber SESAM60 is 50 μJ / cm². 2 ~100 uJ / cm 2 Their damage threshold energy density is approximately between 800 uJ / cm² and 1000 uJ / cm². Based on the above analysis, the preliminary conclusion is that the spot size should ideally be within the middle of this range. Experimental results show that when the spot size is too small, the oscillator's self-mode-locking performance is indeed better, but the mode-locking lifetime of the SESAM becomes very short. For example, when the spot diameter is 4.5 micrometers, the single-point lifetime of the SESAM is only tens to one or two hundred hours. Increasing the spot diameter can effectively extend the single-point lifetime of the SESAM, but as the spot diameter increases, the oscillator's start-up performance decreases until it cannot lock mode. When the spot diameter reaches 8 micrometers or more, the oscillator's self-starting and mode-locking become significantly difficult. If the spot size is taken as the middle value of the range of 4 to 8 micrometers, approximately 6 micrometers, the lifetime of a single working point on the SESAM surface can reach more than 500 hours, or even exceed 1000 hours. At the current level of SESAM technology, such a single-area lifetime is approximately within the longest average lifetime range.

[0082] In some embodiments, the aforementioned second fiber optic oscillator further includes a beam focuser; the beam focuser is disposed between the semiconductor saturable absorber SESAM60 and the beam splitter 50, and is used to focus the light beam incident on the surface of the semiconductor saturable absorber SESAM60 to a predetermined spot size range.

[0083] In some embodiments, due to the special design of the oscillating cavity, although the pump light is a non-polarized signal, the wavelength division combiner 40 in this application is a polarization-maintaining wavelength division combiner.

[0084] In some embodiments, the moving mechanism 70 includes a SESAM base, a one-dimensional moving platform, a stepper motor, and a position sensor;

[0085] The semiconductor saturable absorber SESAM60 is fixedly mounted on the SESAM base. The SESAM base is fixedly connected to the one-dimensional moving platform by bolts. The relative angle between the SESAM base and the one-dimensional moving platform is defined by bolts.

[0086] The output shaft of the stepper motor is coaxially connected to the guide rail shaft of the one-dimensional moving platform. The control terminal of the stepper motor is electrically connected to the seed source control module 12. The seed source control module 12 is used to send the SESAM point switching control command to the stepper motor. After the SESAM point switching control command is configured on the stepper motor, it controls the stepper motor to drive the one-dimensional moving platform to move along the guide rail.

[0087] The position sensor is installed on the one-dimensional moving platform to collect real-time displacement data of the one-dimensional moving platform.

[0088] Understandably, the seed source control module 12 can analyze the stability of the mode-locking state based on the mode-locking feedback signal. If the power attenuation rate of the pulse light fed back by the mode-locking feedback signal is greater than 0.8 dB / hour within N consecutive sampling periods (e.g., N=5, 6, 7), it is determined that the current operating point of the SESAM is showing a deterioration trend and is prone to mode-locking startup failure. A SESAM point-changing control command can be generated and sent to the stepper motor. After the SESAM point-changing control command is configured in the stepper motor, it controls the stepper motor to drive the one-dimensional moving platform to move along the guide rail, thereby moving the operating point of the semiconductor saturable absorber SESAM60 to a new position.

[0089] Optionally, the control program built into the FPGA chip will determine the cause of the failed mode-locking attempts based on the results of several failed attempts. If necessary, it will enable the creation of SESAM switching points and drive the stepper motor to move the semiconductor saturable absorber SESAM60 to the next new working area. Then, it will try the mode-locking self-start or "overshoot" start method.

[0090] Therefore, as can be seen from the programmed control function of the aforementioned Field Programmable Gate Array (FPGA), the reliability of seed source mode-locked oscillation is comprehensively improved due to the implementation of programmed control features, and the startup failure rate can be reduced to the greatest extent. This application integrates the above-mentioned states that ensure seed source mode-locked startup and stable operation, and implements the logic function based on the control process of the programmable FPGA chip. The mechanism for ensuring mode-locked startup is achieved through the coordinated operation of the above three features: within the selected pulse repetition frequency operating region, the seed source itself possesses good mode-locked self-starting performance; when necessary, the control system automatically enables the "overshoot" mode-locked startup mode; when the mode-locking performance of the semiconductor saturable absorber SESAM60 in the current operating region is detected to be deteriorated, the focused beam is automatically switched to a new region to restore the mode-locking performance. The result of this coordination is that the seed source can automatically solve the following typical mode-locked startup failure problems.

[0091] Furthermore, it's worth noting that a single operating point on the SESAM surface, when optimally tuned, can achieve a mode-locked lifetime of up to or exceeding one thousand hours. However, this is far from sufficient to achieve a seed source lifetime exceeding ten thousand hours. Since the mechanism limiting the mode-locked lifetime of SESAMs is not yet fully understood, no solution has yet emerged that addresses this issue from the perspective of SESAM materials. Therefore, a more realistic solution is to enable the switching of the SESAM's operating point. In fiber femtosecond seed sources, the one-dimensional length of the SESAM device is approximately 1 millimeter, while during mode-locked modulation, the beam spot size on the SESAM surface is less than 10 micrometers. If a 25-micrometer-long region is reserved for each operating point, then when using one-dimensional movement to switch the operating point, a currently used SESAM device can provide thirty to forty different operating regions. This would ensure a SESAM device lifetime of tens of thousands of hours.

[0092] like Figure 4 As shown, the one-dimensional moving platform has a stroke of 4 mm, resulting in a very small platform size that meets the volume requirements of our oscillating cavity. Typically, the surface dimensions of the SESAM used in fiber mode-locked lasers are less than 2 mm. The 4 mm stroke ensures the need for continuous point switching. Furthermore, this platform exhibits sufficiently high stability, with lateral fluctuations within a few micrometers during movement. A stepper motor drives the one-dimensional moving platform to precisely position itself with a step accuracy of 0.1 micrometers. Combined with position feedback from a position sensor, accurate positioning is achieved, ensuring that the laser spot accurately falls in the center of the new working area after each switch, avoiding mode-locking instability caused by overlap or offset.

[0093] A key factor for the SESAM spot switching device in a fiber-optic mode-locked oscillator is to ensure that the angle between the SESAM surface and the moving axis of the moving mechanism 70 is 0 or close to 0 (e.g., less than one to two milliradians). To this end, embodiments of this application also design a SESAM base and a one-dimensional moving platform with bolts defining the relative angle between the SESAM base and the one-dimensional moving platform.

[0094] This angle adjustment mechanism, in conjunction with precision fine-tuning bolts, allows for one-time calibration during installation and long-term locking. For example, such as... Figure 5 As shown, one surface of the SESAM base is used to mount the SESAM, and they are connected by machining to form a certain elasticity. The SESAM base includes tension screws 71 and push screws 72. By tightening or loosening the two, the included angle between the SESAM base and the one-dimensional moving platform can be finely adjusted. The SESAM base is also provided with four screw holes 73, which are used to fix the connection with the one-dimensional moving platform.

[0095] Specifically, when adjustment is needed, the SESAM base is secured to the one-dimensional moving platform using screws through any two of the screw holes, while the screws in the other two screw holes are left loose. This allows the angle between the SESAM base and the one-dimensional moving platform, specifically the angle between the front surface of the base and the moving axis, to be adjusted using tension screw 71. After adjustment, the SESAM base is then secured to the one-dimensional moving platform using screws through the two screw holes, thus fixing the angle between the SESAM mounting surface of the base and the moving axis.

[0096] With the aforementioned mechanical structure in place, coarse adjustment of the included angle can be achieved by adjusting it. During this process, the minute height difference between the SESAM base and the surface of the one-dimensional moving platform can be measured using a depth micrometer. This difference is then converted into the included angle deviation, allowing the included angle between the SESAM base surface and the moving axis of the one-dimensional moving platform to be adjusted to zero (the difference in readings is zero). The adjustment process is very easy and smooth. Once the distance difference reading is adjusted to zero, even considering potential errors in the measuring instrument itself, the actual residual angular error remains within 1 milliradian.

[0097] In most cases, this coarsely adjusted SESAM surface is sufficient to meet the requirements for focusing the beam. Based on this, once the beam emitted by the beam focuser is collimated and fixed at a point on the SESAM surface, the beam will shift to different areas of the SESAM surface as the SESAM moves with the moving platform. Because this well-adjusted mechanism ensures that the direction of the focused beam relative to the SESAM and the distance to the focal point remain unchanged, the mode-locking performance of the entire cavity remains constant.

[0098] In some embodiments, although the coarse adjustment described above can ensure that the mode-locking remains unchanged in most cases, there is still a possibility that the residual error after adjustment exceeds the accuracy requirements. Therefore, the SESAM collimation state, a further improvement of the optical collimation method used in the embodiments of this application, can serve as a supplementary collimation method.

[0099] In this application, the optical collimation method is performed during the adjustment of the mode-locked oscillating cavity, which does not conflict with the coarse adjustment process.

[0100] In general, optical collimation adjustment is performed using a continuous light source, such as an amplified spontaneous emission source. However, experiments show that when using such a light source for fine collimation adjustment relative to the SESAM surface, the stability of the light source signal and the limitations imposed by the fluctuations in the SESAM surface's response to the light signal make adjustment inconvenient and the required accuracy difficult to achieve. In contrast, the mode-locked state of the mode-locked oscillator has the most direct relationship with the collimation adjustment of the focused beam relative to the SESAM surface, and exhibits excellent repeatability. Therefore, in the adjustment process of this application, collimation readjustment using an optical signal when necessary is performed during the mode-locking start adjustment process.

[0101] In this embodiment, the relative angle between the SESAM base and the one-dimensional moving platform is obtained by collimating the relative displacement direction of the incident beam focused on the surface of the semiconductor saturable absorber SESAM60 under a preset optimal mode-locked state.

[0102] Specifically, the optical path and mechanical layout during optical collimation adjustment are as follows: Figure 6As shown. After the SESAM base and one-dimensional moving platform have completed coarse adjustment, the beam focuser of the mode-locked oscillating cavity can be adjusted for translation and rotation using a five-dimensional adjustment mechanism. First, the beam is collimated relative to one end of the surface of the semiconductor saturable absorber SESAM60 to achieve the optimal mode-locking state. Then, while keeping other states of the oscillating cavity unchanged, the SESAM is moved to the other end of its surface. If the mode-locking state of the oscillating cavity remains unchanged, it indicates that the coarse adjustment has been completed. If the included angle mentioned in the "coarse adjustment" has not yet reached the required accuracy, the mode-locking state of the SESAM after movement will change significantly. At this time, the distance between the beam focuser and the surface of the semiconductor saturable absorber SESAM60 can be finely adjusted to restore the mode-locking state to the optimal state. By observing the direction of movement of the beam focuser relative to the SESAM surface during this process, the direction of the residual included angle can be determined. That is, by slightly rotating the surface of the semiconductor saturable absorber SESAM60 back and forth, it can be determined whether the residual included angle is positive or negative. Subsequently, the surface is finely adjusted in the direction that can provide compensation, which can gradually reduce and eliminate this residual included angle. Based on the adjustment result, the included angle is fine-tuned again. The adjustment result is checked again using the above method, and adjustments are continued to reduce any remaining included angle to an acceptable range. The adjusted semiconductor saturable absorber SESAM60 and beam focuser are fixed together in the same base plate or housing to ensure their stability and reliability.

[0103] It should be noted that the embodiments of this application adopt a combination of mechanical coarse adjustment and optical collimation for fine adjustment, which can significantly improve the collimation accuracy between SESAM and the incident beam, control the residual angle within ±0.5 arcseconds, and optimize the mode-locking accuracy. This level of accuracy is sufficient to support long-term stable mode-locking of the femtosecond laser.

[0104] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A 1030 nm soliton-type pulsed FP-cavity femtosecond fiber optic oscillator, characterized in that, include: Mold-locked oscillation cavity, pump source, moving mechanism, and seed source control module; The mode-locked oscillator includes a chirped fiber Bragg grating, a ytterbium-doped fiber, a wavelength division multiplexing synthesizer, a beam splitter, and a semiconductor saturable absorber (SESAM). The pump source is connected to the pump port of the wavelength division multiplexing (WDM) combiner, the signal port of the WDM combiner is connected to the ytterbium-doped fiber and the first end of the beam splitter, the ytterbium-doped fiber is connected to the chirped fiber Bragg grating, and the second end of the beam splitter is connected to the semiconductor saturable absorber (SESAM). The pump light emitted from the pump source is coupled into the ytterbium-doped fiber via the wavelength division multiplexing (WDM) combiner. After being amplified by the ytterbium-doped fiber, it forms a gain pulse light. The gain pulse light is then pulse-corrected by the chirped fiber Bragg grating and reflected back into the ytterbium-doped fiber for further gain amplification. The further amplified pulse light passes through the WDM combiner and enters the beam splitter. The beam splitter outputs a portion of the pulse light as a seed source laser output, while the other portion of the pulse light is transmitted to the semiconductor saturable absorber (SESAM) for pulse modulation and reflected back into the mode-locked oscillator cavity to form a soliton pulse. The seed source control module has a built-in FPGA chip. The seed source control module is used to analyze the mode-locked feedback signal of the semiconductor saturable absorber (SESAM), and generate a pump source current adjustment command and a SESAM switching control command based on the mode-locked feedback signal. It is also used to send the pump source current adjustment command to the pump source to adjust the output power of the pump source; and to send the SESAM switching control command to the moving mechanism to drive the moving mechanism to perform a switching operation on the operating point of the semiconductor saturable absorber (SESAM).

2. The 1030 nm soliton-type pulsed FP-cavity femtosecond fiber optic oscillator according to claim 1, characterized in that, Also includes: The first isolator; the two ends of the first isolator are respectively connected to the beam splitter and the first output port, the first output port being used to output seed source laser.

3. The 1030 nm soliton-type pulsed FP-cavity femtosecond fiber optic oscillator according to claim 1, characterized in that, Also includes: A pump drive assembly; the pump drive assembly includes a pump drive module, a signal detector, a second isolator, and a second output port; The two ends of the second isolator are connected to the beam splitter and the second output port, respectively. The second output port is connected to the signal detector, the signal detector is connected to the seed source control module, the seed source control module is connected to the pump drive module, and the pump drive module is connected to the pump source. The signal detector is used to collect the mode-locked feedback signal of the semiconductor saturable absorber (SESAM). The seed source control module is used to generate a pump source current adjustment command based on the mode-locked feedback signal collected by the signal detector and send it to the pump drive module. The pump source current adjustment command is configured after the pump drive module to adjust the current output by the pump drive module to the pump source.

4. The 1030 nm soliton-type pulsed FP-cavity femtosecond fiber optic oscillator according to claim 1, characterized in that, Also includes: A third isolator and a third output port; the two ends of the third isolator are respectively connected to the chirped fiber Bragg grating and the third output port.

5. The 1030 nm soliton-type pulsed FP-cavity femtosecond fiber optic oscillator according to claim 1, characterized in that, The chirped fiber Bragg grating has an anomalous dispersion value of 0.58 picoseconds / nanometer and a spectral bandwidth of 6 to 15 nanometers.

6. The 1030 nm soliton-type pulsed FP-cavity femtosecond fiber optic oscillator according to claim 1, characterized in that, The saturation energy density of the semiconductor saturable absorber (SESAM) is 50 μJ / cm². 2 ~100 uJ / cm 2 .

7. The 1030 nm soliton-type pulsed FP-cavity femtosecond fiber optic oscillator according to claim 1, characterized in that, Also includes: Beam focuser; The beam focuser is disposed between the semiconductor saturable absorber (SESAM) and the beam splitter, and is used to focus the light beam incident on the surface of the semiconductor saturable absorber (SESAM) to a predetermined spot size range.

8. The 1030 nm soliton-type pulsed FP-cavity femtosecond fiber oscillator according to claim 1, characterized in that, The wavelength division combiner is a polarization-maintaining wavelength division combiner.

9. The 1030 nm soliton-type pulsed FP-cavity femtosecond fiber optic oscillator according to claim 3, characterized in that, The moving mechanism includes a SESAM base, a one-dimensional moving platform, a stepper motor, and a position sensor; The semiconductor saturable absorber (SESAM) is fixedly mounted on the SESAM base. The SESAM base is fixedly connected to the one-dimensional moving platform by bolts. The relative angle between the SESAM base and the one-dimensional moving platform is defined by the bolts. The output shaft of the stepper motor is coaxially connected to the guide rail shaft of the one-dimensional moving platform. The control terminal of the stepper motor is electrically connected to the seed source control module. The seed source control module is used to send the SESAM point switching control command to the stepper motor. The SESAM point switching control command is configured after the stepper motor to control the stepper motor to drive the one-dimensional moving platform to move along the guide rail. The position sensor is installed on the one-dimensional moving platform and is used to collect real-time displacement data of the one-dimensional moving platform.

10. The 1030 nm soliton-type pulsed FP-cavity femtosecond fiber oscillator according to claim 9, characterized in that, The relative angle between the SESAM base and the one-dimensional moving platform is obtained by collimating the relative displacement direction of the incident beam focused on the surface of the SESAM under a preset optimal mode-locked state.

Images