Pulse-width adjustable all-fiber laser and pulse-width tuning method

Abstract

The application belongs to the technical field of laser, and proposes a pulse width adjustable all-fiber laser and a pulse width tuning method, which comprises a narrow-band dissipative soliton mode-locked fiber laser seed source, a first optical fiber isolator, a fiber amplifier, a second optical fiber isolator, an optical circulator and a dispersion element arranged along an optical path in sequence. The seed source generates mode-locked pulses with a fixed initial spectral width; the intensity of the nonlinear effect is controlled by adjusting the driving current of the pump source, so as to control the spectral broadening of the pulse in the amplification process, form a variable total spectral width, and perform linear time-frequency mapping on the spectral width through the dispersion element with a fixed group delay dispersion value, so as to finally realize continuous and electrically controlled adjustment of the output pulse width. The whole system adopts an all-fiber structure, has high stability, compact structure and good tuning linearity, and is suitable for industrial processing, sensing and scientific research application scenarios that require flexible pulse width regulation.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and in particular to an all-fiber laser with adjustable pulse width and a pulse width tuning method. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] In the development of modern photonics and laser technology, tunable pulse width fiber lasers have attracted much attention due to their flexible control over output characteristics in the time domain. These lasers can adjust the output pulse width within the picosecond to nanosecond range to meet the different time scale requirements of various physical processes, according to specific application needs. Their applications have widely penetrated into many cutting-edge fields such as precision micromachining, optical communication, nonlinear optics, ultrafast spectroscopy, and lidar. With the maturity of all-fiber structure technology, fiber-based laser systems have demonstrated significant advantages such as high stability, excellent beam quality, compact structure, and maintenance-free operation, becoming the mainstream choice in industrial and scientific research scenarios. In recent years, advancements in mode-locking technology, nonlinear effect modulation, and dispersion management have further promoted the development of high-performance tunable pulse width light sources, making it possible to achieve complex pulse shaping and control through fiber optic devices.

[0004] Existing tunable pulse-width fiber lasers still face numerous technical bottlenecks in their practical application. Some solutions rely on complex tunable filter structures integrated within the cavity, which not only increases system cost but also makes them sensitive to environmental disturbances, affecting long-term operational stability. Another type of system based on a "stretch-amplify-compress" architecture can obtain high-energy pulses, but its large structure and reliance on mechanical adjustment make it difficult to achieve rapid electronic control and continuous tuning. In addition, while directly modulated semiconductor lasers have the advantage of convenient electronic control, they are limited by issues such as the lower limit of pulse width, low peak power, and poor resistance to backlighting. Overall, current technical approaches generally suffer from drawbacks such as complex structures, inflexible tuning, and difficulty in balancing performance and cost. There is an urgent need for a new pulse-width tunable laser solution that combines an all-fiber structure, a wide tuning range, high stability, and ease of operation. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a pulse-width-tunable all-fiber laser and a pulse-width tuning method. It ingeniously combines the stability of narrowband dissipative soliton mode-locking, the controllability of nonlinear spectral broadening during fiber amplification, and the dispersion broadening effect of chirped gratings. Through a simple "seed-amplification-broadening" linear link, the width of the final output pulse can be continuously controlled by adjusting only the single electrical parameter of the amplifier's pump power.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides an all-fiber laser with adjustable pulse width.

[0008] A pulse-width tunable all-fiber laser includes a narrowband dissipative soliton mode-locked fiber laser seed source, a first fiber isolator, a fiber amplifier, a second fiber isolator, an optical circulator, and a dispersive element arranged sequentially in the direction of light propagation. The fiber amplifier includes a pump source, a bundle combiner, and a gain fiber.

[0009] The seed source of the narrowband dissipative soliton mode-locked fiber laser is used to generate a seed pulse with an initial spectral width. The first fiber isolator is used to transmit the received seed pulse to the beam combiner. The seed pulse and the pump light generated by the pump source are combined by the beam combiner and enter the gain fiber. During the amplification process, the spectral broadening is generated due to nonlinear effects and is controlled by the driving current of the pump source. The sum of the spectral broadening and the initial spectral width is the total spectral width.

[0010] The first port of the optical circulator is connected to the second fiber isolator, the second port of the optical circulator is connected to the input port of the dispersive element, and the third port of the optical circulator serves as the output end of the all-fiber laser. The dispersive element has a fixed group delay dispersion value, which is used to linearly map pulses with different total spectral widths to the corresponding output pulse widths. The total spectral width is controlled by the driving current of the pump source, thereby indirectly and linearly controlling the pulse width output from the third port of the optical circulator.

[0011] In one implementation of the first aspect of the present invention, a narrowband dissipative soliton mode-locked fiber laser seed source is used to generate a laser with a center wavelength in a preset band, a repetition frequency of a set value, and an initial pulse width of [value missing]. and the initial spectral width is Seed pulse.

[0012] As a further limitation of the first aspect of the invention, the spectral broadening amount Nonlinear phase shift accumulated in the gain fiber by the seed pulse Proportional, nonlinear phase shift and ,in, These are nonlinear coefficients. The peak power of the seed pulse. The effective length of action;

[0013] The gain is changed by adjusting the drive current of the pump source, which in turn changes the peak power of the seed pulse. Spectral broadening Perform continuous control.

[0014] As a further limitation of the first aspect of the invention, the total spectral width for: The expanded pulse width is: , and This output pulse width is a fixed value. With total spectral width Proportional to each other, thus outputting the pulse width It has a monotonic relationship with the drive current of the pump source.

[0015] In one implementation of the first aspect of the present invention, the fiber amplifier is a single-stage amplification structure, a two-stage amplification structure, or a multi-stage amplification structure.

[0016] In a two-stage or multi-stage amplification structure, at least the pump power of the last stage amplifier is used as a control parameter for pulse width tuning, and isolators or filters are added between stages to suppress spontaneous radiation of the amplification.

[0017] The gain fiber is an erbium-doped fiber, a ytterbium-doped fiber, or a thulium-doped fiber that matches the wavelength of the seed pulse.

[0018] In one implementation of the first aspect of the present invention, the beam combining element is a beam combiner or a wavelength division multiplexer, and the group delay dispersion value of the dispersive element is selected according to the target pulse width tuning range.

[0019] In one implementation of the first aspect of the present invention, the dispersive element is a chirped fiber grating, a long-distance single-mode fiber, a dispersion-compensating fiber module, or a spatial grating pair.

[0020] In one implementation of the first aspect of the present invention, a pulse selection module is arranged between the second isolator and the first port of the optical circulator. The pulse selection module is an optical fiber coupled electro-optic modulator or acousto-optic modulator, driven by an external radio frequency signal, and is used to select a single pulse or a pulse with a reduced repetition frequency from a pulse sequence with a high repetition frequency.

[0021] In one implementation of the first aspect of the present invention, the output of the all-fiber laser is connected to an adjustable attenuator.

[0022] Secondly, the present invention provides a pulse width tuning method.

[0023] A pulse width tuning method, utilizing the pulse width-tunable all-fiber laser of the first aspect of the present invention, includes the following steps:

[0024] Start the seed source of the narrowband dissipative soliton mode-locked fiber laser and output a stable seed pulse;

[0025] Set an initial drive current for the pump source in the fiber amplifier. This amplifies the seed pulse and produces a certain spectral broadening.

[0026] The amplified and broadened light pulse is introduced into the dispersive element through the optical circulator. After being broadened in the time domain, the light pulse is emitted from the output port of the optical circulator.

[0027] Measure or apply the width of the current output pulse ;

[0028] If you need to change the width of the output pulse to the target value Then, based on the pre-calibrated or theoretically calculated relationship curve between the pump current and the width of the output pulse, the drive current of the pump source is adjusted to the corresponding... ;

[0029] After the system stabilizes, the output pulse width is The output pulse.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] (1) The present invention has a simple structure and low cost. The present invention abandons the complex intracavity tuning structure and multi-stage compression system, and only adopts the mature linear structure of "seed source-amplifier-fixed dispersion broadener". All core components (mode-locked seed source, pump LD, WDM, isolator, circulator, chirped grating) are standard commercial fiber optic devices, and there is no need to customize expensive adjustable delay lines or grating pairs. The system has high integration, simple assembly and adjustment, and the overall cost is far lower than the existing solutions.

[0032] (2) The tuning method of this invention is extremely simple and fast. The pulse width tuning of this invention is achieved by adjusting the driving current of a single pump source. This is a purely electrical operation with no mechanical moving parts, and the tuning response speed is fast (depending on the response time of the pump LD current driving circuit, typically on the order of microseconds), enabling rapid switching or scanning of the pulse width. The user interface is user-friendly and easy to integrate with a computer control system to achieve automated and programmed control.

[0033] (3) The tuning range of the present invention is wide and continuous. By reasonably selecting the dispersion of the chirped grating and the nonlinear broadening capability of the amplifier, continuous tuning from the picosecond level to the nanosecond level can be easily achieved; for example, in specific implementation cases, continuous tuning from about 10 ps to more than 1 ns has been achieved, and theoretically it can be extended to more than 1 ns through optimization, which covers the main application range from short pulse processing to long pulse welding.

[0034] (4) The present invention has excellent output performance. Good beam quality: The all-fiber structure ensures consistent single-mode, near-diffraction-limited beam output (M²≈1.1); High stability: The all-fiber enclosed structure is not sensitive to environmental vibration, temperature fluctuations, dust and other interference. The seed source mode-locking is stable, the pump power adjustment is stable, and the overall long-term power stability of the system is better than 1% (RMS).

[0035] (5) High practicality and scalability. Easy power calibration: The average output power and pulse energy can be improved while maintaining the pulse width tuning function by upgrading the pump power of the amplifier and the gain fiber; Wide wavelength adaptability: The principle of this scheme is applicable to different wavelengths (such as 1μm, 1.5μm, 2μm), and only the seed source, gain fiber and chirped grating of the corresponding wavelength need to be replaced; Other functions can be integrated: It is easy to integrate additional modulators (such as those for pulse selection down-conversion) in the optical path or cascade them with subsequent power amplifiers to build a more powerful tunable pulse width laser system.

[0036] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0037] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0038] Figure 1 A schematic diagram of a pulse-width-tunable fiber laser provided as an exemplary embodiment of the present invention, wherein the optical path is indicated by arrows in the figure;

[0039] Figure 2 A schematic diagram of the output laser pulse power under different pump powers is provided as an exemplary embodiment of the present invention;

[0040] Figure 3 A schematic diagram of the spectrum of a seed pulse provided as an exemplary embodiment of the present invention;

[0041] Figure 4 A schematic diagram of the pulse width of a seed pulse provided for an exemplary embodiment of the present invention;

[0042] Figure 5 A schematic diagram of the spectral width when the pump power is 170mW, provided as an exemplary embodiment of the present invention;

[0043] Figure 6 A schematic diagram of the spectral width when the pump power is 280mW, provided as an exemplary embodiment of the present invention;

[0044] Figure 7 A schematic diagram of the spectral width when the pump power is 500mW, provided as an exemplary embodiment of the present invention;

[0045] Figure 8 A schematic diagram of the spectral width when the pump power is 750mW, provided as an exemplary embodiment of the present invention;

[0046] Figure 9 A schematic diagram of the pulse width when the pump power is 170mW, provided as an exemplary embodiment of the present invention;

[0047] Figure 10 A schematic diagram of the pulse width when the pump power is 280mW, provided as an exemplary embodiment of the present invention;

[0048] Figure 11 A schematic diagram of the pulse width when the pump power is 500mW, provided as an exemplary embodiment of the present invention;

[0049] Figure 12 A schematic diagram of the pulse width when the pump power is 750mW, provided as an exemplary embodiment of the present invention;

[0050] Figure 13 A schematic diagram of the structure of a pulse-width-tunable fiber laser with an added pulse selection module, provided in an exemplary embodiment of the present invention;

[0051] Among them, 101 is the seed source of the narrowband dissipative soliton mode-locked fiber laser; 102 is the first fiber isolator; 103 is the pump source; 104 is the wavelength division multiplexer; 105 is the gain fiber; 106 is the second fiber isolator; 107 is the optical circulator; 108 is the chirped fiber grating; 109 is the laser output end; and 110 is the pulse selection module. Detailed Implementation

[0052] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0053] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0054] This implementation proposes a pulse-width-tunable fiber laser based on the principle of "pump power-controlled spectral-dispersion mapping pulse width". The core idea is to generate a stable, narrow-spectrum seed pulse using a dissipative soliton mode-locked laser; actively control the spectral broadening caused by nonlinear effects (mainly self-phase modulation) during pulse amplification by adjusting the pump power of the subsequent fiber amplifier; then injecting the broadened spectral pulse into a chirped fiber grating with a fixed dispersion. Since the group delay of the chirped grating is linearly related to the wavelength, the spectral width directly determines the pulse broadening in the time domain. Therefore, by electrically adjusting the pump power to control the spectral width, the final output pulse width can be indirectly and linearly controlled.

[0055] The following is a brief introduction to the technical terms and related concepts involved in this treatment plan, including:

[0056] Dissipative soliton mode-locking: a stable ultrashort pulse operating mechanism formed in fiber lasers with positive or near-zero net cavity dispersion. It is characterized by a relatively regular spectral shape (usually Gaussian or parabolic), a relatively wide temporal pulse width (typically on the picosecond scale), and high pulse energy, exhibiting strong nonlinearity and dispersion balance within the cavity. Dissipative solitons are insensitive to intracavity perturbations, making stable mode-locking easy to achieve, and are often used as high-quality seed sources for high-power amplification systems.

[0057] Chirped fiber Bragg gratings (FBGs) are fiber Bragg gratings whose refractive index modulation period gradually varies along the fiber axis. Because light of different wavelengths is reflected at different positions within the grating, it experiences different optical path lengths, thus introducing a wavelength-dependent group delay, i.e., dispersion, during reflection (or transmission). The large dispersion can be used to effectively stretch or compress optical pulses in the time domain.

[0058] Optical circulator: A multi-port (typically three-port) non-reciprocal optical device. Optical signals can only be transmitted sequentially from the first port to the second port, and from the second port to the third port, and cannot be transmitted in reverse. In this invention, it is used to guide amplified optical pulses into a chirped grating and to guide the pulses, broadened by reflection from the grating, to the output terminal, while simultaneously achieving optical isolation.

[0059] Fiber optic amplifier: A device that uses a section of fiber doped with rare earth elements (such as erbium, ytterbium, thulium, etc.) as the gain medium and amplifies the power of a signal under pump light excitation. Its amplification process is accompanied by certain nonlinear effects, such as self-phase modulation, which can lead to signal spectral broadening.

[0060] Specifically, such as Figure 1 As shown, the optical path includes, in sequence, the following components: a narrowband dissipative soliton mode-locked fiber laser seed source 101, a first fiber isolator 102, a fiber amplifier (including a pump source 103, a wavelength division multiplexer 104, and a gain fiber 105), a second fiber isolator 106, an optical circulator 107, and a chirped fiber grating 108. The generated laser is output from the laser output end 109.

[0061] In this implementation, the narrowband dissipative soliton mode-locked fiber laser seed source 101 is used to generate a laser with a center wavelength in a preset band (such as 1μm, 1.5μm, 2μm, etc.) and a repetition frequency of 1. The initial pulse width is (Typical value 5-100 ps), with narrow spectral width A stable optical pulse sequence (typically <5nm). This seed source is typically an all-fiber structure, employing nonlinear amplifying ring mirrors, nonlinear polarization rotation, or semiconductor saturable absorbers to achieve dissipative soliton mode-locking. Its net cavity dispersion is positive or close to zero to ensure the formation of dissipative solitons.

[0062] To provide clearer guidance for engineering practice, taking the 1.5-micron band as an example, a typical narrowband dissipative soliton seed source can be constructed as follows: A ring cavity structure is used, containing a section of approximately 1 meter long erbium-doped fiber (EDF) as the gain medium. Two wavelength division multiplexers (WDMs) of 980 / 1550 nm are connected to either side of the EDF to couple the 980 nm pump light. An isolator (PI-ISO) is also included within the cavity to force unidirectional light transmission, which is fundamental for achieving stable mode locking. The most critical part is the mode-lock initiation and maintenance mechanism. If a nonlinear polarization rotation (NPR) scheme is used, two polarization controllers (PC1, PC2) and a polarization-dependent isolator (PD-ISO) or polarizer must be precisely placed within the cavity. By finely adjusting these two polarization controllers, intensity-dependent loss, i.e., an equivalent saturable absorption effect, can be artificially introduced into the cavity. When the pump power exceeds a threshold, this nonlinear loss suppresses intracavity noise, allowing high-intensity pulses to pass through smoothly, thus spontaneously forming and stabilizing the mode-locked state. In this state, observations using an OSA spectrometer show a spectrum that is typically flat-topped or approximately rectangular, with a bandwidth between 1 and 3 nm, characteristic of dissipative solitons. The corresponding time-domain pulse width, measured by an autocorrelator, is typically on the order of 10–30 ps. The advantages of this seed source lie in its relatively simple structure, low cost, and high output pulse energy, making it ideal for subsequent nonlinear spectral broadening.

[0063] Another robust approach is to use a real saturable absorber, such as a semiconductor saturable absorber mirror (SESAM). SESAMs are commercially available devices with fast recovery times, high damage thresholds, and stable performance. Integrating a SESAM into one end of a linear or toroidal cavity allows for highly reliable mode-locking initiation and maintenance. While SESAMs are more expensive than polarization controllers in the NPR approach, their troubleshooting-free and high-stability characteristics make them more attractive for industrial applications. Regardless of the mode-locking mechanism used, the core specifications of the seed source must be guaranteed (i.e., narrow spectrum, picosecond pulse width, and high stability), as these are fundamental to the success of the entire pulse width tuning scheme. If the seed pulse itself is unstable or has an excessively wide spectrum, the effect of subsequent spectral broadening through pump power adjustment will be significantly reduced, or even prevent linear mapping from being achieved.

[0064] The narrowband dissipative soliton mode-locked fiber laser seed source 101 of this implementation can be achieved using different mode-locking mechanisms, including but not limited to: nonlinear amplifying ring mirror mode-locking, nonlinear polarization rotation mode-locking, and mode-locking based on real saturable absorbers (such as semiconductor saturable absorber mirrors SESAM, carbon nanotubes, graphene, topological insulators, and other two-dimensional materials), as long as its output pulse characteristics conform to the characteristics of dissipative solitons in the narrow spectrum and positive dispersion region.

[0065] The output wavelength of the narrowband dissipative soliton mode-locked fiber laser seed source 101 can be selected as needed, for example: 1550 nm band for erbium-doped fiber systems, 1030-1080 nm band for ytterbium-doped fiber systems, 1900-2000 nm band for thulium-doped fiber systems, etc.; correspondingly, the operating wavelengths of all passive devices in the system (isolators, wavelength division multiplexers (or bundle combiners), circulators, chirped gratings) need to be matched and adjusted.

[0066] In practical applications, the choice of wavelength is often determined by the target application scenario. For example, in the field of precision micromachining, the 1-micron band (ytterbium-doped fiber) is widely used due to its high absorption rate in metallic materials; while in ophthalmic medical applications or the processing of certain special materials (such as polymers), the 1.5-micron or 2-micron bands are preferred due to their strong absorption characteristics in water. Furthermore, the 1.5-micron band is also the C-band of optical fiber communication, offering natural advantages for applications in the field of optical communication. Therefore, the universality of this invention lies in its architecture not being dependent on a specific wavelength; it only requires "changing the components." However, it should be noted that the fiber nonlinearity coefficient varies in different wavelength regions (…). There are differences in the available dispersive elements and the required optical fibers. For example, standard single-mode fiber (SMF-28) near the 1.5-micron wavelength is close to zero dispersion, with a small dispersion value and a relatively high nonlinear coefficient; while in the 1-micron band, standard fiber has a larger dispersion value (approximately 20 ps / nm / km) and a slightly lower nonlinear coefficient. These differences in physical parameters directly affect the efficiency of spectral broadening in the amplifier and the required dispersion of the chirped grating. Therefore, in specific designs, detailed link simulations must be performed for the target wavelength to determine the optimal gain fiber length, pump power range, and chirped grating parameters.

[0067] In this implementation, the first fiber optic isolator 102 is connected after the seed source to prevent reverse optical feedback from subsequent stages from entering the seed source, thus ensuring the long-term stability of the seed source operation.

[0068] In this implementation, the fiber amplifier includes a pump source 103, a wavelength division multiplexer 104 (or a combiner), and a section of rare-earth-doped gain fiber 105. The input end of the gain fiber 105 receives a seed pulse from the first fiber isolator 102 and pump light from the pump source 103 via the wavelength division multiplexer 104 (or combiner). The pump source 103 is a current-tunable semiconductor laser or a fiber laser. Under pump light excitation, the seed pulse receives power amplification in the gain fiber, and its spectrum broadens due to nonlinear effects (mainly self-phase modulation). The spectral broadening amount... Nonlinear phase shift accumulated in the optical fiber with the pulse Proportional, and ,in, These are nonlinear coefficients. For pulse peak power, This refers to the effective operating length. The gain can be changed by adjusting the drive current of the pump source, thereby altering the peak power of the pulse. This allows for the achievement of spectral broadening. Continuous control.

[0069] In this implementation, preferably, the fiber amplifier is a single-stage preamplifier, designed to achieve sufficient spectral broadening and tuning range while avoiding excessive nonlinearity or damage risks introduced by over-amplification. The gain fiber can be selected from erbium-doped fiber, ytterbium-doped fiber, or thulium-doped fiber, etc., matched to the seed wavelength.

[0070] Optionally, in other implementations, the fiber amplifier may employ a two- or multi-stage amplification structure to achieve higher gain and nonlinear broadening. In multi-stage amplification, the pump power of at least the last stage amplifier is used as a control parameter for pulse width tuning. Isolators or filters may be added between stages to suppress spontaneous emissions from the amplification.

[0071] In this implementation, the type of gain fiber can be matched with the seed wavelength, such as erbium-doped fiber, ytterbium-doped fiber, thulium-doped fiber, or thulium-holmium co-doped fiber. The gain fiber can be single-clad or double-clad (when cladding pumping is used).

[0072] In this implementation, the pump source can be pumped in the same direction, in the opposite direction, or in both directions.

[0073] In this implementation, the second fiber optic isolator 106 is located after the fiber optic amplifier and is used to isolate subsequent optical path reflections and protect the amplifier.

[0074] In this implementation, the optical circulator 107 has a first port, a second port, and a third port, and the output of the second fiber optic isolator is connected to the first port of the optical circulator.

[0075] In this implementation, the input of the chirped fiber grating 108 is connected to the second port of the optical circulator. This chirped fiber grating 108 is designed for the center wavelength of the seed laser and has high reflectivity (>90%) and a fixed group delay dispersion value D (unit: ps / nm). When the spectral width is... When a pulse is incident, different wavelength components are reflected within the grating and experience different time delays, causing the pulse to be broadened in the time domain. The broadened pulse width is approximately: .because and It is fixed, therefore the output pulse width is... With total spectral width Proportional to, and thus to, the amplifier pump power (control). They form a monotonic correspondence.

[0076] In this implementation, preferably, the dispersion factor D of the chirped fiber grating is selected based on the target pulse width tuning range. For example, if the target is to tune from 10 ps to 1 ns, and the spectral tuning range is assumed to be 2 nm to 20 nm, then the required dispersion factor D is approximately Commercially available chirped fiber gratings with corresponding dispersion values ​​can be selected.

[0077] The core fixed-dispersion element, the chirped fiber grating 108, in this implementation can be replaced by other devices that can provide fixed, known group delay dispersion. For example, a long stretch of single-mode fiber can be broadened using its material dispersion. However, the required fiber is typically very long, the dispersion is relatively small, and additional nonlinearity may be introduced. Dispersion compensation fiber modules, commercially available fixed-dispersion DCF modules, and spatial grating pairs, although not all-fiber, can be used in some systems that allow spatial optical paths to provide fixed dispersion, sacrificing all-fiber characteristics but potentially achieving greater dispersion. The key point is that the dispersion value D of this dispersion element is fixed during tuning, and the pulse width variation is entirely caused by a controllable change in spectral width at the front end.

[0078] In this implementation, the third port of the optical circulator serves as the laser output terminal 109 of the pulse-width tunable fiber laser, used to output tunable pulse-width laser pulses after being broadened by a chirped fiber grating.

[0079] In this implementation, optionally, an adjustable attenuator can be added after the final output to independently control the energy or average power of the output pulse without affecting the pulse width. In many applications, users need to adjust not only the pulse width but also the output energy independently. For example, in material processing, for the same material, it may be necessary to fix the pulse width but adjust the energy to control the processing depth. If the energy is changed only by adjusting the pump current, the pulse width will also change, which is obviously not suitable. Therefore, integrating a fiber-coupled adjustable optical attenuator (VOA) after the laser output 109 is a very practical extension. The VOA can be based on MEMS technology or on thermo-optic or electro-optic effects. By controlling the attenuation of the VOA with an external electrical signal, the output power can be adjusted over a wide range (e.g., 30 dB) while keeping the pulse width constant. This "pulse width-energy" decoupled control greatly enhances the application flexibility of the system.

[0080] Optionally, in other implementations, a real-time pulse width monitoring module (such as a high-speed photodetector with an oscilloscope or autocorrelation instrument) can be integrated and used to form a closed-loop feedback with the pump current control circuit to achieve automatic stabilization and precise setting of the output pulse width. The specific scheme for achieving closed-loop control can be constructed as follows:

[0081] (1) Monitoring Module Setup: A small portion of the light from the main output optical path is split off as a monitoring signal through a low splitting ratio (e.g., 1%-5%) fiber optic coupler. This portion of light is fed into a high-speed photodetector (PD), whose bandwidth must be much higher than the frequency components of the pulse to be measured. For example, to accurately measure a 10 ps pulse, the PD's bandwidth needs to be at least 35 GHz. The PD converts the optical pulse into an electrical signal.

[0082] (2) Signal Processing and Analysis: The electrical signal is fed into a high-bandwidth real-time oscilloscope. The oscilloscope's sampling rate and bandwidth also need to be matched. The embedded processor inside the oscilloscope or an external computer extracts the current pulse width in real time by running a specific algorithm (e.g., calculating the full width at half maximum (FWHM) of the pulse). .

[0083] (3) Feedback control loop: the extracted The value is fed into a proportional-integral-derivative (PID) controller. The PID controller will... With the target pulse width set by the user The comparison is performed, and the error signal is calculated. Based on this error signal, the PID controller outputs a corrected control voltage. This drives the current drive circuit of pump source 103.

[0084] (4) System workflow: When the user sets a new target pulse width At this time, the system first provides an initial pump current value based on the pre-stored open-loop "pump current-output pulse width" look-up table (LUT). This LUT is obtained through comprehensive calibration before the system leaves the factory, and it records the corresponding output pulse width under different pump currents.

[0085] Subsequently, the closed-loop control circuit begins operation. The monitoring module measures the actual output pulse width in real time. And it feeds back to the PID controller. If and If a deviation occurs (e.g., due to ambient temperature drift, device aging, or power supply fluctuations), the PID controller will immediately calculate a correction and fine-tune the pump current until... Stable at Within the allowable error range (e.g., ±1%).

[0086] This closed-loop architecture can effectively suppress various external disturbances and internal drift, ensuring that the output pulse width remains stable at the set value over a long period of time. Users do not need to worry about the complex nonlinear physical processes at the underlying level. They only need to input the target pulse width, and the system will automatically complete all adjustments. Even if the performance of the laser changes slowly over time (such as a decrease in gain fiber efficiency), the closed-loop system can compensate through continuous feedback to maintain output consistency.

[0087] In this implementation, preferably, the pump source is equipped with a digital or analog control interface to receive external control signals in order to achieve precise and programmed adjustment of the pump power, thereby automatically setting the output laser pulse width.

[0088] like Figure 2 As shown, a schematic diagram of the output laser pulse power under different pump powers is presented; as... Figure 3 and Figure 4 The image shows a schematic diagram of the spectrum and pulse width of the seed pulse, as shown below. Figure 5 , Figure 6 , Figure 7 and Figure 8 The figure shows the spectral width of the amplified laser at different pump powers (170mW, 280mW, 500mW, and 750mW). Figure 9 , Figure 10 , Figure 11 and Figure 12 As shown, the laser pulse width after grating broadening is obtained under different pump powers (170mW, 280mW, 500mW and 750mW). It can be seen that as the pump power increases, the output laser spectrum broadens from 0.15nm to 2.5nm, and the laser pulse width also gradually broadens from 12ps to 1.2ns after broadening.

[0089] Based on the aforementioned pulse-width tunable fiber laser, this implementation proposes a pulse-width tuning method based on the laser, comprising the following steps:

[0090] Step S1301: Start the seed source of the narrowband dissipative soliton mode-locked fiber laser to output a stable narrow-spectrum pulse sequence.

[0091] Step S1302: Set an initial drive current for the pump source in the fiber amplifier. This amplifies the seed pulse and produces a certain spectral broadening.

[0092] Step S1303: The amplified and broadened optical pulse is introduced into the chirped fiber grating through the optical circulator. After being broadened in the time domain, the pulse is emitted from the output end of the optical circulator.

[0093] Step S1304: Measure or apply the width of the current output pulse. .

[0094] Step S1305: If it is necessary to change the output pulse width to the target value Then, based on the pre-calibrated or theoretically calculated "pump current-output pulse width" relationship curve, the drive current of the pump source is adjusted to the corresponding... .

[0095] Step S1306: Return to step S1303. Once the system stabilizes, the output pulse width is... Laser pulses.

[0096] By continuous change This allows for the output pulse width to be achieved. Continuous tuning within the range determined by the dispersion of the chirped fiber grating.

[0097] Optionally, in other implementations, pump power control can be achieved through analog voltage, digital signals, or microprocessor-based PID control algorithms; the correspondence between "pump current and output pulse width" can be established by creating a lookup table through a one-time system calibration, or it can be calculated in real time based on a theoretical model; the tuning process can be open-loop control or closed-loop control combined with pulse width monitoring.

[0098] Optionally, in some other implementations, such as Figure 13 Between the second fiber isolator 106 and the optical circulator 107, a pulse selection module 110 is added. The pulse selection module 110 can be a fiber-coupled electro-optic modulator or acousto-optic modulator, driven by an external radio frequency signal, used to select a single pulse or a pulse with a reduced repetition frequency from a high repetition frequency pulse sequence to meet the needs of some applications that require low repetition frequency and high single pulse energy.

[0099] In summary, this study provides a compact, easily integrated, simple to operate, and reliable pulse-width tunable laser source, facilitating its introduction into the industrial and scientific research markets. It avoids the use of complex intracavity tunable filter structures or multi-stage "broadening-amplification-compression" chains, reducing system complexity and manufacturing costs. Furthermore, it offers a method for achieving wide-range, continuous pulse width tuning without the need for precise mechanical adjustments, relying solely on a single electrical parameter (pump current). While achieving wide-range pulse width tuning, it maintains excellent beam quality, spectral characteristics, and the inherent high stability of the all-fiber system. This breakthrough overcomes the tuning limitations of some existing solutions in the picosecond range, enabling a leapfrog tuning from the picosecond to the nanosecond level, covering a wider range of application needs.

[0100] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A pulse-width-tunable all-fiber laser, characterized in that, The system includes a narrowband dissipative soliton mode-locked fiber laser seed source, a first fiber isolator, a fiber amplifier, a second fiber isolator, an optical circulator, and a dispersive element arranged sequentially in the direction of light propagation. The fiber amplifier includes a pump source, a bundle combiner, and a gain fiber. The narrowband dissipative soliton mode-locked fiber laser seed source is used to generate a seed pulse with an initial spectral width. The first fiber isolator is used to transmit the received seed pulse to the beam combiner. The seed pulse and the pump light generated by the pump source are combined by the beam combiner and enter the gain fiber. During the amplification process, a spectral broadening amount controlled by the driving current of the pump source is generated due to nonlinear effects. The sum of the spectral broadening amount and the initial spectral width is the total spectral width. The first port of the optical circulator is connected to the second fiber isolator, the second port of the optical circulator is connected to the input port of the dispersive element, and the third port of the optical circulator serves as the output end of the all-fiber laser. The dispersive element has a fixed group delay dispersion value, which is used to linearly map pulses with different total spectral widths to the corresponding output pulse widths. The total spectral width is controlled by the driving current of the pump source, thereby indirectly and linearly controlling the pulse width output from the third port of the optical circulator. Spectral broadening Nonlinear phase shift accumulated in the gain fiber by the seed pulse Proportional, nonlinear phase shift and Proportional, of which, These are nonlinear coefficients. The peak power of the seed pulse. The effective length of action; The gain is changed by adjusting the drive current of the pump source, thereby altering the peak power of the seed pulse. Spectral broadening Perform continuous control.

2. The pulse-width-tunable all-fiber laser as described in claim 1, characterized in that, The narrowband dissipative soliton mode-locked fiber laser seed source is used to generate a center wavelength in a preset band, a repetition frequency of a set value, and an initial pulse width of [value missing]. and the initial spectral width is Seed pulse.

3. The pulse-width-tunable all-fiber laser as described in claim 1, characterized in that, Total spectral width for: The expanded pulse width is: , and This output pulse width is a fixed value. With total spectral width Proportional to each other, thus outputting the pulse width It has a monotonic correspondence with the driving current of the pump source.

4. The pulse-width-tunable all-fiber laser as described in any one of claims 1-3, characterized in that, The fiber amplifier can be a single-stage amplification structure, a two-stage amplification structure, or a multi-stage amplification structure. In a two-stage or multi-stage amplification structure, at least the pump power of the last stage amplifier is used as a control parameter for pulse width tuning, and isolators or filters are added between stages to suppress spontaneous radiation of the amplification. The gain fiber is an erbium-doped fiber, a ytterbium-doped fiber, or a thulium-doped fiber that matches the wavelength of the seed pulse.

5. The pulse-width-tunable all-fiber laser as described in any one of claims 1-3, characterized in that, The beam combining element is a beam combiner or a wavelength division multiplexer, and the group delay dispersion value of the dispersive element is selected according to the target pulse width tuning range.

6. The pulse-width-tunable all-fiber laser as described in any one of claims 1-3, characterized in that, The dispersion element is a chirped fiber grating, a long section of single-mode fiber, a dispersion-compensating fiber module, or a spatial grating pair.

7. The pulse-width-tunable all-fiber laser as described in any one of claims 1-3, characterized in that, A pulse selection module is arranged between the second fiber isolator and the first port of the optical circulator. The pulse selection module is a fiber-coupled electro-optic modulator or acousto-optic modulator driven by an external radio frequency signal, used to select a single pulse or a pulse with a reduced repetition frequency from a pulse sequence with a high repetition frequency.

8. The pulse-width-tunable all-fiber laser as described in any one of claims 1-3, characterized in that, The output of the all-fiber laser is connected to an adjustable attenuator.

9. A pulse width tuning method, characterized in that, The pulse-width tunable all-fiber laser according to any one of claims 1-8 comprises the following process: The narrowband dissipative soliton mode-locked fiber laser seed source is activated, and a stable seed pulse is output. Set an initial drive current for the pump source in the fiber amplifier. This amplifies the seed pulse and produces a certain spectral broadening. The amplified and broadened light pulse is introduced into the dispersive element through the optical circulator, and the light pulse is broadened in the time domain and emitted from the output port of the optical circulator. Measure or apply the width of the current output pulse ; If you need to change the width of the output pulse to the target value Then, based on the pre-calibrated or theoretically calculated relationship curve between the pump current and the width of the output pulse, the drive current of the pump source is adjusted to the corresponding... ; After the system stabilizes, the output pulse width is The output pulse.

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