Fiber laser and laser pulse state tuning method

Abstract

The invention discloses an optical fiber laser and a laser pulse state tuning method, and relates to the technical field of ultrafast laser, the optical fiber laser comprises an optical resonant cavity, a polarization controller, a polarization-maintaining wavelength division multiplexer, a first polarization-maintaining optical fiber isolator, a second polarization-maintaining optical fiber isolator and a polarization-maintaining single-mode semiconductor pump laser; the optical resonant cavity comprises a mode-locked laser generation module and a tuning module, and can generate mode-locked laser in various mode-locked states; the polarization controller is used for adjusting the polarization state of the pump light or the mode-locked laser, the polarization-maintaining wavelength division multiplexer is used for multiplexing and demultiplexing the pump light or the mode-locked laser, and the polarization-maintaining optical fiber isolator ensures one-way propagation of the light. The internal parameters of the laser are directly regulated and controlled through the temperature tuning or angle tuning module, the complexity of external light path adjustment is avoided, the high repetition frequency of mode-locked laser pulses and the long-term stability of the laser in the long-time operation process are ensured, and the diversified requirements of different application fields for the performance of an ultrafast laser light source are met.

Description

Technical Field

[0001] The present application relates to the field of ultrafast laser technology, and in particular to a fiber laser and a laser pulse state tuning method. Background Art

[0002] Ultrafast laser technology, with its unique picosecond to femtosecond pulse widths, high peak power, and high temporal resolution, plays a vital role in numerous high-tech fields, including but not limited to ultrafast spectroscopy, nonlinear microscopy, precision micro- and nanofabrication, and ultrahigh-speed optical communications. These properties make ultrafast lasers an ideal tool for exploring dynamic processes within matter, achieving high-precision processing, and high-speed data transmission.

[0003] With the continuous advancement of science and technology, the performance requirements of ultrafast laser light sources in various application fields are increasing, especially in terms of flexible control of parameters such as pulse duration, peak power, and polarization state. Precise control of these parameters is crucial to achieving specific application effects. However, the ultrafast laser light source control technology in related technologies usually relies on parameters in the external optical path to control the pulse state, which increases the complexity and size of the system and cannot directly control the characteristics of the light source itself, resulting in limitations in switching between different soliton states and adapting to various application requirements.

[0004] Therefore, there is an urgent need for a fiber laser and a laser pulse state tuning method that can flexibly control the pulse output characteristics to ensure the high repetition frequency of the mode-locked laser pulse and the long-term stability of the laser during long-term operation. Summary of the Invention

[0005] The purpose of this application is to provide a fiber laser and laser pulse state tuning method that can overcome the limitations of related technologies and meet the needs of light sources in multiple fields such as high-speed optical communications, high-precision laser processing, biomedical imaging, lidar, and ultrafast spectroscopy. The laser can flexibly control the pulse output characteristics, ensuring a high repetition rate of mode-locked laser pulses and long-term stability of the laser during long-term operation.

[0006] To achieve the above objectives, this application provides the following solutions:

[0007] In a first aspect, the present application provides a fiber laser, comprising:

[0008] Optical resonant cavity, polarization controller, polarization-maintaining wavelength division multiplexer, first polarization-maintaining fiber isolator, second polarization-maintaining fiber isolator, polarization-maintaining single-mode semiconductor pump laser;

[0009] The optical resonant cavity includes a mode-locked laser generating module and a tuning module for generating mode-locked lasers in different mode-locked states; the mode-locked laser generating module is used to generate the mode-locked laser; the tuning module is a temperature tuning module or an angle tuning module, used to tune the mode-locked state of the mode-locked laser; the mode-locked state includes a birefringence-managed soliton output mode, a dislocation vector asymmetric soliton molecular output mode, a pulse-splitting birefringence-managed soliton output mode, and a stripe soliton output mode;

[0010] One end of the polarization controller is connected to the optical resonant cavity, and the other end is connected to one end of the polarization-maintaining wavelength division multiplexer, and is used to adjust the polarization state of the pump light or the mode-locked laser;

[0011] The other end of the polarization-maintaining wavelength division multiplexer is connected to one end of the first polarization-maintaining optical fiber isolator and the second polarization-maintaining optical fiber isolator, respectively, for multiplexing and demultiplexing the pump light or the mode-locked laser;

[0012] The first polarization-maintaining fiber isolator and the second polarization-maintaining fiber isolator are used to ensure unidirectional propagation of pump light and mode-locked laser respectively;

[0013] The polarization-maintaining single-mode semiconductor pump laser is connected to the other end of the first polarization-maintaining optical fiber isolator and is used to provide pump light.

[0014] In a second aspect, the present application provides a laser pulse state tuning method, comprising:

[0015] An optical resonant cavity is prepared using polarization-maintaining gain fiber and polarization-maintaining passive fiber;

[0016] Using a polarization-maintaining single-mode semiconductor pump laser, the pump light passes through a first polarization-maintaining fiber isolator, then through a polarization-maintaining wavelength division multiplexer and a polarization controller, and is input into an optical resonant cavity to obtain an initial mode-locked laser.

[0017] Tuning the initial mode-locked laser by a tuning method to obtain a mode-locked laser in a target mode-locked state; the tuning method includes a temperature tuning method or an angle tuning method;

[0018] The mode-locked laser in the target mode-locked state is output through a polarization controller, a polarization-maintaining wavelength division multiplexer, and a second polarization-maintaining optical fiber isolator.

[0019] According to the specific embodiments provided in this application, this application has the following technical effects:

[0020] The present application provides a fiber laser and a method for tuning the laser pulse state. By integrating an optical resonant cavity, a polarization controller, a polarization-maintaining wavelength division multiplexer, a first polarization-maintaining fiber isolator, a second polarization-maintaining fiber isolator, and a polarization-maintaining single-mode semiconductor pump laser, the limitations of traditional ultrafast lasers in pulse state control are solved, and flexible control and efficient switching of mode-locked laser pulses are achieved. By setting a mode-locked laser generation module and a temperature tuning or angle tuning module in the optical resonant cavity, the problems of high system complexity and large volume caused by relying on external optical path adjustment in the prior art are solved, and direct control of the mode-locked laser state (such as birefringence management solitons, dislocation vector asymmetric soliton molecules, pulse splitting birefringence management solitons, and stripe solitons, etc.) is achieved, thereby improving the system's integration and stability. Through the synergistic effect of the polarization controller and the polarization-maintaining wavelength division multiplexer, the problem of the difficulty in accurately controlling the polarization state of the pump light and the mode-locked laser is solved, and flexible adjustment and efficient multiplexing and demultiplexing of the polarization state are achieved, further improving the performance and application flexibility of the laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0022] Figure 1 A schematic diagram of the functional modules of a fiber laser provided in one embodiment of the present application;

[0023] Figure 2 A schematic flow chart of a laser pulse state tuning method provided in one embodiment of the present application;

[0024] Figure 3 This is a schematic diagram of the results of laser pulse states at different temperatures based on the temperature tuning method provided in one embodiment of the present application; wherein, Figure 3 (a) is a schematic diagram of the laser pulse state at a temperature of 15°C; Figure 3 (b) is a schematic diagram of the laser pulse state at a temperature of 25°C; Figure 3 (c) is a schematic diagram of the laser pulse state at a temperature of 35°C; Figure 3 (d) is a schematic diagram of the laser pulse state at a temperature of 45°C;

[0025] Figure 4 This is a schematic diagram of the results of laser pulse states at different polarization angles based on the angle tuning method provided in one embodiment of the present application; wherein, Figure 4(a) is a schematic diagram of the results of laser pulse states with polarization angles ranging from 0.2π to 0.31π; Figure 4 (b) is a schematic diagram of the results of the laser pulse state with a polarization angle of 0.35π to 0.36π;

[0026] Figure 4 (c) is a schematic diagram of the laser pulse state with a polarization angle of 0.33π; Figure 4 (d) is a schematic diagram of the laser pulse state with a polarization angle of 0.34π;

[0027] Figure 5 Schematic diagram of the typical autocorrelation trajectory of the output mode of the misaligned vector asymmetric soliton molecule;

[0028] Figure 6 Schematic diagram of a typical spectrum of soliton output modes managed by birefringence for pulse splitting;

[0029] Figure 7 Schematic diagram of the typical autocorrelation trajectory of the stripe soliton output mode.

[0030] Figure 1: 1-polarization-maintaining single-mode semiconductor pump laser; 2-first polarization-maintaining fiber isolator; 3-second polarization-maintaining fiber isolator; 4-polarization-maintaining wavelength division multiplexer; 5-polarization controller; 6-dichroic dielectric film; 7-polarization-maintaining gain fiber; 8-polarization-maintaining passive fiber; 9-semiconductor saturable absorber mirror; 10-packaging component; 11-semiconductor refrigerator; 12-thin-film heating resistor; 13-temperature sensing unit; 14-first rotating platform; 15-second rotating platform; 16-laser output end. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0032] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0033] In an exemplary embodiment, Figure 1 As shown, a fiber laser is provided, comprising:

[0034] Optical resonant cavity, polarization controller 5, polarization-maintaining wavelength division multiplexer 4, first polarization-maintaining fiber isolator 2, second polarization-maintaining fiber isolator 3, polarization-maintaining single-mode semiconductor pump laser 1.

[0035] The optical resonator includes a mode-locked laser generation module and a tuning module for generating mode-locked lasers in different mode-locked states. The mode-locked laser generation module is used to generate the mode-locked laser. The tuning module is a temperature tuning module or an angle tuning module for tuning the mode-locked state of the mode-locked laser. The mode-locked states include birefringence-managed soliton output modes, misalignment vector asymmetric soliton molecular output modes, pulse-splitting birefringence-managed soliton output modes, and stripe soliton output modes. The optical resonator is a birefringence-managed Fabry-Perot optical resonator fabricated by fusion splicing a polarization-maintaining gain fiber 7 with a polarization-maintaining passive fiber 8. It is used to generate high-repetition-rate lasers exceeding 1 GHz and possesses multiple output states.

[0036] One end of the polarization controller 5 is connected to the optical resonant cavity, and the other end is connected to one end of the polarization-maintaining wavelength division multiplexer 4 , and is used to adjust the polarization state of the pump light or the mode-locked laser.

[0037] The other end of the polarization-maintaining wavelength division multiplexer 4 is connected to one end of the first polarization-maintaining fiber isolator 2 and the second polarization-maintaining fiber isolator 3 respectively, for multiplexing and demultiplexing the pump light or the mode-locked laser.

[0038] The first polarization-maintaining fiber isolator 2 and the second polarization-maintaining fiber isolator 3 are used to ensure unidirectional propagation of the pump light and the mode-locked laser, respectively.

[0039] The polarization-maintaining single-mode semiconductor pump laser 1 is connected to the other end of the first polarization-maintaining optical fiber isolator to provide pump light.

[0040] The fiber laser is used to generate GHz-level high repetition frequency laser light in the 1 μm band and output the laser light through the laser output terminal 16 .

[0041] As an optional implementation, the mode-locked laser generating module specifically includes: a polarization-maintaining gain fiber 7 , a polarization-maintaining passive fiber 8 , a semiconductor saturable absorber mirror 9 and a dichroic dielectric film 6 .

[0042] The semiconductor saturable absorber mirror 9 is coupled to one end of the polarization-maintaining passive optical fiber 8 .

[0043] The dichroic dielectric film 6 is coupled to one end of the polarization-maintaining gain optical fiber 7 .

[0044] The other end of the polarization-maintaining gain optical fiber 7 is connected to the other end of the polarization-maintaining passive optical fiber 8 by fusion splicing.

[0045] As an optional implementation, the optical resonant cavity further includes a packaging component 10 .

[0046] When the tuning module is a temperature tuning module, the mode-locked laser generating module is located inside the packaging component 10 , and the temperature tuning module is fixed on the packaging component 10 .

[0047] When the tuning module is an angle tuning module, both the mode-locked laser generating module and the angle tuning module are located inside the packaging component 10 .

[0048] In this embodiment, when the tuning module is a temperature tuning module, the temperature tuning module includes: a semiconductor cooling plate 11 , a thin film heating resistor 12 and a temperature sensing unit 13 .

[0049] The semiconductor refrigeration plate 11 , the thin film heating resistor 12 and the temperature sensing unit 13 are respectively connected to the polarization-maintaining single-mode semiconductor pump laser 1 through wires.

[0050] The temperature sensing unit 13 is fixed to the inside of the packaging component behind the other end of the semiconductor saturable absorber mirror 9 and is used to monitor the temperature of the optical resonant cavity in real time.

[0051] The semiconductor refrigeration sheet 11 is fixed on the outside of the packaging component 10 above the polarization-maintaining gain optical fiber 7 and is used to cool the optical resonant cavity.

[0052] The thin-film heating resistor 12 is fixed to the exterior of the packaging assembly 10 to the side of the polarization-maintaining gain fiber 7 and is used to heat the optical resonant cavity. The temperature sensing unit 13 is used to monitor the ambient temperature of the birefringence-managed Fabry-Perot optical resonant cavity in real time. The semiconductor cooling plate 11 is used to reduce or stabilize the ambient temperature of the birefringence-managed Fabry-Perot optical resonant cavity. The thin-film heating resistor 12 is used to increase or stabilize the ambient temperature of the birefringence-managed Fabry-Perot optical resonant cavity.

[0053] As an optional implementation, the temperature sensing unit 13 may be a thermistor.

[0054] The birefringence-managed Fabry-Perot optical resonator consists of a polarization-maintaining gain fiber 7, a polarization-maintaining passive fiber 8, a semiconductor saturable absorber mirror 9, and a dichroic dielectric film 6, and is used to generate GHz high-repetition-rate mode-locked lasers in multiple mode-locked states; the semiconductor saturable absorber mirror 9 is coupled to the polarization-maintaining passive fiber 8 to reduce the energy density reaching the end face of the semiconductor saturable absorber mirror, thereby improving the repeatable self-start life and long-term stability of the fiber laser; the dichroic dielectric film 6 is coupled to the polarization-maintaining gain fiber 7 and connected to the polarization-maintaining wavelength division multiplexer 4 via the polarization-maintaining single-mode fiber 7; the polarization-maintaining gain fiber 7 and the polarization-maintaining passive fiber 8 are connected by fusion splicing.

[0055] In this embodiment, when the tuning module is an angle tuning module, the angle tuning module includes: a first polarization angle adjustment submodule and a second polarization angle adjustment submodule.

[0056] The first polarization angle adjustment submodule is used to adjust the position of the dichroic dielectric film 6 .

[0057] The second polarization angle adjustment submodule is used to adjust the position of the polarization-maintaining gain optical fiber 7 .

[0058] As an optional implementation, the first polarization angle adjustment submodule includes a first rotating platform 14 ; the second polarization angle adjustment submodule includes a second rotating platform 15 .

[0059] In this embodiment, the first polarization angle adjustment submodule and the second polarization angle adjustment submodule both further include a standard optical fiber ceramic ferrule.

[0060] The first rotating platform 14 is connected to the dichroic dielectric film 6 via a standard optical fiber ceramic ferrule.

[0061] The second rotating platform 15 is connected to the semiconductor saturable absorber mirror 9 via a standard optical fiber ceramic ferrule.

[0062] Based on the same inventive concept, the present application also provides a method for tuning the laser pulse state using the aforementioned fiber laser. The solution provided by this method is similar to the solution described in the aforementioned method. Therefore, the specific limitations of one or more of the following embodiments of the laser pulse state tuning method can be found in the above-mentioned limitations on fiber lasers and will not be further elaborated here.

[0063] In an exemplary embodiment, Figure 3 As shown, a laser pulse state tuning method is provided, comprising the following steps 201 to 208. In which:

[0064] In step 201 , an optical resonant cavity is prepared using a polarization-maintaining gain fiber 7 and a polarization-maintaining passive fiber 8 .

[0065] In step 202 , a polarization-maintaining single-mode semiconductor pump laser 1 is used to transmit pump light through a first polarization-maintaining fiber isolator 2 , a polarization-maintaining wavelength division multiplexer 4 , and a polarization controller 5 , and then input the pump light into an optical resonant cavity to obtain an initial mode-locked laser.

[0066] Step 203 , tuning the initial mode-locked laser by a tuning method to obtain a mode-locked laser in a target mode-locked state; the tuning method includes a temperature tuning method or an angle tuning method.

[0067] In step 204 , the mode-locked laser in the target mode-locked state is output from the laser output end 16 through the polarization controller 5 , the polarization-maintaining wavelength division multiplexer 4 , and the second polarization-maintaining fiber isolator 3 .

[0068] By implementing the above steps 201 to 204, the present application can achieve flexible tuning and efficient switching of the mode-locked laser pulse state, significantly improving the application flexibility and performance of fiber lasers in the field of ultrafast laser technology.

[0069] In another exemplary embodiment of the present application, when the tuning method in step 203 is a temperature tuning method, tuning the initial mode-locked laser by the tuning method to obtain a mode-locked laser in a target mode-locked state specifically includes:

[0070] The target temperature range of the optical resonant cavity is determined based on the mode-locked laser in the target mode-locked state.

[0071] The current temperature of the optical resonant cavity is lowered to the target temperature by the semiconductor refrigeration sheet 11 , or the current temperature of the optical resonant cavity is raised to the target temperature by the thin film heating resistor 12 ; the target temperature is any temperature within the target temperature range.

[0072] Use the following formula to calculate the birefringence of the first polarization-maintaining fiber:

[0073]

[0074] ΔT=T0-T.

[0075] Among them, B T represents the birefringence index of the first polarization-maintaining fiber; C(λ) represents the photoelastic coefficient, which is related to the wavelength; E represents Young's modulus; γ represents Poisson's ratio; ε represents the core ellipticity. The polarization-maintaining fibers in this embodiment are all panda-type polarization-maintaining fibers, and the ideal value of their core ellipticity is generally 1; Δα represents the difference between the cladding linear expansion coefficient and the stress axis linear expansion coefficient; ΔT represents the temperature difference; T0 represents the fiber melting temperature; and T represents the target temperature.

[0076] The propagation constant difference of the first orthogonal polarization component is calculated based on the birefringence coefficient of the first polarization-maintaining fiber using the following formula:

[0077]

[0078] Among them, Δβ T represents the propagation constant difference of the first orthogonal polarization component; λ is the mode-locked laser wavelength in the mode-locked state.

[0079] It is determined whether the propagation constant difference of the first orthogonal polarization component is within a first preset propagation constant difference range to obtain a determination result.

[0080] If the judgment result is yes, a mode-locked laser in the target mode-locked state is obtained.

[0081] If the judgment result is no, the target temperature is adjusted and the process returns to step "lowering the current temperature of the optical resonant cavity to the target temperature through the semiconductor refrigeration plate 11, or raising the current temperature of the optical resonant cavity to the target temperature through the thin film heating resistor 12".

[0082] A mode-locked pulse, a steady-state solution to the Ginzburg-Landau equation under the combined effects of dispersion, birefringence, self-phase modulation, cross-phase modulation, gain, and loss, exhibits a spatiotemporal evolution determined by the dynamic balance between the equation's nonlinear effects, dispersion, gain and loss, and the high birefringence of the polarization-maintaining fiber. This balance ensures the pulse remains stable as it circulates within the cavity, corresponding to the steady-state solution of the equation. Changes in the propagation constant difference of the first orthogonal polarization components directly affect the group velocity difference and coupling behavior of the components. This further influences the pulse's energy distribution through nonlinear effects such as cross-phase modulation, altering the phase matching condition and causing the mode-locked state to switch from one steady-state solution to the Ginzburg-Landau equation (e.g., birefringence-managed solitons) to another (e.g., dislocation-vector asymmetric solitons), thus achieving mode-locked state switching.

[0083] In another exemplary embodiment of the present application, when the tuning method in step 203 is an angle tuning method, tuning the initial mode-locked laser by the tuning method to obtain a mode-locked laser in a target mode-locked state specifically includes:

[0084] The target polarization angle range of the optical resonant cavity is determined according to the mode-locked laser in the target mode-locked state.

[0085] The current polarization angle is adjusted to the target polarization angle by the first rotating platform 14 and the second rotating platform 15 to obtain a mode-locked laser in a target mode-locked state; the target polarization angle is any polarization angle within the target polarization angle range.

[0086] In polarization-maintaining fibers, light propagates along two orthogonal directions: the slow axis (s-axis) and the fast axis (f-axis). These two directions have different propagation characteristics. When light propagates in an optical resonator and forms a mode-locked laser, changes in the polarization angle affect the energy distribution of the light along the slow and fast axes of the polarization-maintaining fiber.

[0087] The following formula is used to calculate the orthogonal polarization component of the slow axis of the polarization-maintaining fiber and the orthogonal polarization component of the fast axis of the polarization-maintaining fiber:

[0088]

[0089] Among them, u s and u f They represent the orthogonal polarization components of the slow axis (s-axis) and the fast axis (f-axis) of the polarization-maintaining fiber, respectively; u x Indicates the orthogonal polarization component of the light propagation direction; u y Indicates that x The orthogonal polarization component in the vertical direction; θ represents the target polarization angle.

[0090] As can be seen from the above formula, changes in the polarization angle θ directly lead to changes in the orthogonal polarization components along the slow and fast axes. When the polarization angle θ varies, the energy distribution ratios along the slow and fast axes differ, which in turn affects properties such as nonlinear effects within the optical resonator. These changes in properties alter the propagation and interaction of the orthogonal polarization components within the resonator, leading to different mode-locked states.

[0091] Therefore, by adjusting the polarization angle to different angles within the target polarization angle range, mode-locked lasers with different mode-locked states can be obtained to meet diverse application needs.

[0092] Through the angle tuning module, the polarization angle is adjusted to change the coupling strength and interference behavior of the orthogonal polarization components, thereby switching the mode-locked state of the total pulse.

[0093] In another exemplary embodiment of the present application, a method for utilizing temperature to tune the state of high-repetition-rate laser pulses is provided. The temperature-controlled tuning module includes a semiconductor refrigeration plate 11, a thin-film heating resistor 12, and a temperature sensing unit 13, which are used to regulate or stabilize the temperature of a birefringence-managed Fabry-Perot optical resonant cavity to achieve tuning of the high-repetition-rate laser pulse state. The semiconductor refrigeration plate 11, the thin-film heating resistor 12, and the temperature sensing unit 13 are connected to a polarization-maintaining single-mode semiconductor pump laser 1 via wires and fixed to a package assembly 10. The temperature control program inherent in the polarization-maintaining single-mode semiconductor pump laser 1 is utilized to achieve real-time temperature monitoring and heating or cooling operations of the birefringence-managed Fabry-Perot optical resonant cavity. The temperature sensing unit 13 is used to monitor the temperature of the ultrashort optical resonant cavity in real time. The semiconductor refrigeration plate 11 is used to lower the temperature of the ultrashort optical resonant cavity to a minimum of 10°C, and the thin-film heating resistor 12 is used to raise the temperature of the ultrashort optical resonant cavity to a maximum of 75°C. The combined action of the semiconductor refrigeration chip 11, the thin-film heating resistor 12, and the temperature sensing unit 13 stabilizes the temperature of the ultrashort optical resonator at any value between 10°C and 75°C, with a temperature fluctuation of less than ±0.2°C. The temperature difference ΔT is used to alter the birefringence coefficient of the first polarization-maintaining fiber of the polarization-maintaining gain fiber 7 and the polarization-maintaining passive fiber 8, thereby changing the propagation constant difference of the orthogonal polarization components, regulating the coupling strength and interference behavior between the two components, and thus switching the mode-locked state of the total pulse.

[0094] The results of the laser pulse state at different temperatures based on the temperature tuning method are shown in the figure. Figure 3 shown; among them, Figure 3 (a) is a schematic diagram of the laser pulse state at a temperature of 15°C; Figure 3 (b) is a schematic diagram of the laser pulse state at a temperature of 25°C; Figure 3 (c) is a schematic diagram of the laser pulse state at a temperature of 35°C; Figure 3(d) is a schematic diagram of the results of the laser pulse state at a temperature of 45°C.

[0095] As an optional embodiment, the fiber laser for implementing the tuning method includes a polarization-maintaining single-mode semiconductor pump laser 1, a first polarization-maintaining fiber isolator 2, a second polarization-maintaining fiber isolator 3, a polarization-maintaining wavelength division multiplexer 4, a polarization controller 5, and a birefringence-managed Fabry-Perot optical resonant cavity, which are connected in sequence through a polarization-maintaining single-mode fiber, and are used to generate a high repetition rate laser greater than 1 GHz with multiple mode-locked states and output it through a laser output end 16.

[0096] The birefringence-managed Fabry-Perot optical resonator includes a dichroic dielectric film 6, a polarization-maintaining gain fiber 7, a polarization-maintaining passive fiber 8, and a semiconductor saturable absorber mirror 9. The semiconductor saturable absorber mirror 9 comprises a semiconductor saturable absorber and a reflector. Within the laser's ultrashort optical resonator, laser pulses circulate back and forth through the semiconductor saturable absorber. When the incident laser pulse intensity is low, the semiconductor saturable absorber has a large absorption coefficient, effectively absorbing the incident beam and reducing the laser gain. However, when the laser pulse intensity reaches a certain threshold, the semiconductor saturable absorber gradually reaches saturation, and the absorption effect weakens. Once saturated, the semiconductor saturable absorber releases the absorbed energy in an extremely short time, maintaining a high-intensity output for a short period of time. Due to this rapid temporal response, the laser pulse can reach extremely high intensity within a very short time. Simultaneously, during this process, the laser pulse within the laser resonator is compressed, resulting in an ultrashort laser pulse on the order of femtoseconds.

[0097] Polarization-maintaining gain fiber 7 provides optical gain in the laser, amplifying the optical signal. A polarization-maintaining single-mode semiconductor pump laser 1 inputs energy into the polarization-maintaining gain fiber 7, exciting the rare-earth dopant ions within it into an excited state. These excited rare-earth dopant ions interact with the laser signal, releasing energy and generating photons of the same frequency as the laser signal, thereby amplifying the signal. The laser signal circulates back and forth through the polarization-maintaining gain fiber 7 within the ultrashort optical resonant cavity, where it is continuously amplified by the rare-earth dopant ions within the fiber, ultimately achieving higher power.

[0098] The first polarization-maintaining fiber isolator 2 prevents the output light from returning to the polarization-maintaining single-mode semiconductor pump laser 1, while the second polarization-maintaining fiber isolator 3 prevents the output light from returning to the polarization-maintaining wavelength division multiplexer 4, thereby protecting the laser oscillator. Fiber isolators utilize the Faraday rotation effect and the directional control of optical devices to ensure that the polarization directions of the input and output optical signals remain different. Reverse-propagating polarized light cannot pass through the fiber isolator and is instead absorbed or reflected, achieving unidirectional transmission and isolation of optical signals, thereby preventing interference and damage to the laser caused by reverse-propagating light signals.

[0099] The polarization-maintaining wavelength division multiplexer 4 combines multiple optical signals of different wavelengths into a single optical fiber for transmission through appropriate wavelength selection. During transmission, the optical signals of different wavelengths in the fiber do not interfere with each other. At the receiving end, the wavelength division multiplexer's counterpart uses wavelength-selective splitters to separate and demultiplex these optical signals, directing them to their corresponding receiving devices for processing, thus preventing interference between the optical signals. The polarization-maintaining wavelength division multiplexer 4 effectively utilizes the optical fiber bandwidth, thereby increasing the system's transmission capacity.

[0100] The polarization controller 5 changes the refractive index and anisotropy of the optical fiber by applying external mechanical stress or stretching different parts of the optical fiber. By adjusting the applied stress, the propagation speed of each polarization mode in the optical fiber changes, thereby controlling the polarization state of the optical fiber output light.

[0101] Polarization-maintaining passive fiber 8 is introduced into a birefringence-managed Fabry-Perot optical resonant cavity by fusion splicing it with polarization-maintaining gain fiber 7 using a fusion splicer. One end of polarization-maintaining gain fiber 8 and one end of polarization-maintaining gain fiber 7 are inserted into a standard fiber optic ceramic ferrule, protecting the fusion splice while using a sleeve to couple to the dichroic dielectric film 6 and semiconductor saturable absorber mirror 9, respectively. Polarization-maintaining passive fiber 8 can reduce the energy of the laser pulse reaching the semiconductor saturable absorber mirror 9, reducing the accumulated thermal damage to the semiconductor saturable absorber mirror 9, extending the number of reusable restarts of the laser, and improving long-term operational stability. The polarization-maintaining gain fiber 7, polarization-maintaining passive fiber 8, and dichroic dielectric film 6 together create a special birefringence environment within the resonant cavity to form lasers with multiple output states. The specific principles are as follows:

[0102] During propagation, a laser pulse can be decomposed into two orthogonal polarization components in the x- and y-directions. When the laser pulse passes through the interfaces between the dichroic dielectric coating 6 and the polarization-maintaining gain fiber 7, and between the polarization-maintaining gain fiber 7 and the polarization-maintaining passive fiber 8, the polarization components along the x- and y-directions undergo mode coupling due to the misalignment angles between the polarization-maintaining gain fiber 7 and the dichroic dielectric coating 6, and between the polarization-maintaining gain fiber 7 and the polarization-maintaining passive fiber 8. These components are then re-decomposed into two orthogonal polarization components along the fast and slow axes of the polarization-maintaining gain fiber 7 or the polarization-maintaining passive fiber 8 and continue to propagate. If the birefringence of the polarization-maintaining gain fiber 7 and the polarization-maintaining passive fiber 8 changes, the mode coupling behavior between the components will be altered, resulting in changes in the laser pulse's spectrum, energy, pulse shape, and repetition rate.

[0103] In this embodiment, the GHz high repetition rate laser includes four output modes, namely birefringence managed soliton output, misalignment vector asymmetric soliton molecular output, pulse splitting birefringence managed soliton output and stripe soliton output. The typical autocorrelation trajectory diagram of the misalignment vector asymmetric soliton molecular output mode is shown in Figure 2. Figure 5 The typical spectrum diagram of the birefringence-managed soliton output mode of pulse splitting is shown in Figure 6 The typical autocorrelation trajectory diagram of the stripe soliton output mode is shown in Figure 7 shown.

[0104] As an optional embodiment, the fiber laser also includes a packaging component 10. The packaging component 10 encapsulates the birefringence-managed Fabry-Perot optical resonant cavity by designing a metal shell, thereby reducing the interference of the external environment on the laser device and facilitating the addition of a temperature tuning module.

[0105] In another exemplary embodiment of the present application, an operating method for utilizing angle tuning of high repetition rate laser pulse states is provided for different operating environments.

[0106] As an optional embodiment, the angle tuning module consists of two parts: a first rotating platform 14, which is fixed to a standard optical fiber ceramic ferrule coupled to the dichroic dielectric film 6; and a second rotating platform 15, which is fixed to a standard optical fiber ceramic ferrule coupled to the semiconductor saturable absorber mirror 9. The first rotating platform 14 and the second rotating platform 15 cooperate to dynamically adjust the axial angle between the polarization-maintaining gain fiber 7 and the dichroic dielectric film 6. In order to avoid damaging the end face of the dichroic dielectric film 6 during the adjustment process, the output of the polarization-maintaining single-mode semiconductor pump laser 1 must be turned off first. Subsequently, the first rotating platform 14 and the second rotating platform 15 rotate in coordination according to the set angle to ensure that the optical fiber in the resonant cavity is not twisted. The rotation range is 0-360° and the rotation accuracy is 1°. After rotating into place (i.e., rotating to the set rotation angle), the output of the polarization-maintaining single-mode semiconductor pump laser 1 is restored. Through the above-mentioned control method, the polarization angle can be accurately adjusted while ensuring safety.

[0107] The polarization angle control mechanism can effectively change the coupling strength and interference behavior of the orthogonal polarization components, thereby switching the mode-locked state of the total pulse, providing greater flexibility and adjustability for optimizing laser output characteristics. The schematic diagram of the laser pulse state at different polarization angles based on the angle tuning method is shown in the figure below. Figure 4 shown; among them, Figure 4 (a) is a schematic diagram of the results of the laser pulse state with a polarization angle of 0.2π to 0.31π, which presents the laser pulse state of birefringence managed solitons. Figure 4 (b) is a schematic diagram of the results of the laser pulse state with a polarization angle of 0.35π to 0.36π, showing the laser pulse state of the misalignment vector asymmetric soliton molecule. Figure 4 (c) is a schematic diagram of the laser pulse state with a polarization angle of 0.33π, showing the laser pulse state of birefringence-managed solitons with pulse splitting. Figure 4(d) is a schematic diagram of the laser pulse state with a polarization angle of 0.34π, showing the laser pulse state of stripe solitons.

[0108] In summary, in response to the problems of single ultrafast laser mode and insufficient tuning flexibility in related technologies, this application proposes a multi-physical field control mechanism, which utilizes the temperature sensitivity of the birefringence coefficient of the polarization-maintaining fiber to tune the high-repetition-rate laser pulse state through precise temperature control; based on the angle between the pulse propagation direction and the fast axis of the polarization-maintaining fiber, that is, the control effect of the polarization angle on the orthogonal polarization component, an angle tuning module is constructed to tune the high-repetition-rate laser pulse state, so that while achieving GHz repetition rate laser output, various pulse modes such as birefringence managed solitons and dislocation vector asymmetric soliton molecules can be stably generated, significantly improving the mode freedom and operation stability, and providing a new light source solution for multi-scenario applications.

[0109] The present application also provides an application scenario, which applies the above-mentioned laser pulse state tuning method. Specifically: the laser pulse state tuning method provided in this embodiment can be applied in precision micro-nano processing scenarios. The precision micro-nano processing scenario includes a material pretreatment link, a high-precision processing link and a post-processing link; the material enters the high-precision processing link from the material pretreatment link, obtains a high-precision micro-nano structure after being irradiated by a mode-locked laser pulse, and enters the post-processing link. The laser pulse state tuning method provided in this embodiment is applied to the high-precision processing link in precision micro-nano processing. Specifically, by tuning the pulse state of the mode-locked laser (such as birefringence managed solitons, dislocation vector asymmetric soliton molecules, etc.), the processing accuracy and efficiency can be optimized to meet the processing requirements of different materials and structures.

[0110] This application has the following beneficial effects:

[0111] 1. A method for using temperature to tune the state of high-repetition-rate laser pulses is proposed. Based on the characteristic that the birefringence coefficient of polarization-maintaining fiber changes with the ambient temperature, combined with the relationship between the propagation constant difference of orthogonal polarization components and the birefringence coefficient, the temperature-dependent birefringence coefficient is regulated, the propagation constant difference of the orthogonal polarization components is changed, and the coupling strength and interference behavior between the two components are regulated, thereby switching the mode-locked state of the total pulse.

[0112] 2. A method for angle-tuning the state of high-repetition-rate laser pulses is proposed. By controlling the pulse propagation direction and the polarization angle of the fast axis of the polarization-maintaining fiber, the coupling strength and interference behavior of the orthogonal polarization components are changed, thereby switching the mode-locked state of the total pulse.

[0113] 3. The birefringence-managed Fabry-Perot optical resonator constructed with polarization-maintaining gain fiber and polarization-maintaining passive fiber has good repeatable self-starting performance and long-term operation stability. It can generate and output GHz high-repetition-rate lasers in various states, including birefringence-managed solitons, misaligned vector asymmetric soliton molecules, pulse-splitting birefringence-managed solitons, and stripe solitons.

[0114] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0115] This document uses specific examples to illustrate the principles and implementation methods of this application. The description of the above examples is only intended to help understand the method and core concept of this application. At the same time, for those skilled in the art, based on the concept of this application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A fiber laser, characterized in that: The fiber laser comprises: an optical resonant cavity, a polarization controller, a polarization-maintaining wavelength division multiplexer, a first polarization-maintaining fiber isolator, a second polarization-maintaining fiber isolator, and a polarization-maintaining single-mode semiconductor pump laser; The optical resonant cavity includes a mode-locked laser generating module and a tuning module for generating mode-locked lasers in different mode-locked states; the mode-locked laser generating module is used to generate the mode-locked laser; the tuning module is a temperature tuning module or an angle tuning module, used to tune the mode-locked state of the mode-locked laser; the mode-locked state includes a birefringence-managed soliton output mode, a dislocation vector asymmetric soliton molecular output mode, a pulse-splitting birefringence-managed soliton output mode, and a stripe soliton output mode; One end of the polarization controller is connected to the optical resonant cavity, and the other end is connected to one end of the polarization-maintaining wavelength division multiplexer, and is used to adjust the polarization state of the pump light or the mode-locked laser; The other end of the polarization-maintaining wavelength division multiplexer is connected to one end of the first polarization-maintaining optical fiber isolator and the second polarization-maintaining optical fiber isolator, respectively, for multiplexing and demultiplexing the pump light or the mode-locked laser; The first polarization-maintaining fiber isolator and the second polarization-maintaining fiber isolator are used to ensure unidirectional propagation of pump light and mode-locked laser respectively; The polarization-maintaining single-mode semiconductor pump laser is connected to the other end of the first polarization-maintaining optical fiber isolator and is used to provide pump light.

2. The fiber laser according to claim 1, wherein: The mode-locked laser generation module specifically includes: a polarization-maintaining gain fiber, a polarization-maintaining passive fiber, a semiconductor saturable absorber mirror, and a dichroic dielectric film; The semiconductor saturable absorber mirror is coupled to one end of a polarization-maintaining passive optical fiber; The dichroic dielectric film is coupled to one end of a polarization-maintaining gain optical fiber; The other end of the polarization-maintaining gain optical fiber is connected to the other end of the polarization-maintaining passive optical fiber by fusion splicing.

3. The fiber laser according to claim 1, wherein: The optical resonant cavity further includes a packaging component; When the tuning module is a temperature tuning module, the mode-locked laser generating module is located inside the packaging component, and the temperature tuning module is fixed on the packaging component; When the tuning module is an angle tuning module, both the mode-locked laser generating module and the angle tuning module are located inside the packaging component.

4. The fiber laser according to claim 1, wherein: The temperature tuning module includes: a semiconductor refrigeration chip, a thin film heating resistor and a temperature sensing unit; The semiconductor refrigeration sheet, the thin film heating resistor and the temperature sensing unit are respectively connected to the polarization-maintaining single-mode semiconductor pump laser through wires; The temperature sensing unit is fixed to the inside of the package component behind the other end of the semiconductor saturable absorber mirror and is used to monitor the temperature of the optical resonant cavity in real time; The semiconductor refrigeration sheet is fixed on the outside of the packaging component above the polarization-maintaining gain optical fiber, and is used to cool the optical resonant cavity; The thin film heating resistor is fixed on the outside of the packaging component on the side of the polarization-maintaining gain optical fiber, and is used to heat the optical resonant cavity.

5. The fiber laser according to claim 1, wherein: The angle tuning module includes: a first polarization angle adjustment submodule and a second polarization angle adjustment submodule; The first polarization angle adjustment submodule is used to adjust the position of the dichroic dielectric film; The second polarization angle adjustment submodule is used to adjust the position of the polarization-maintaining gain optical fiber.

6. The fiber laser according to claim 5, characterized in that The first polarization angle adjustment submodule includes a first rotating platform; the second polarization angle adjustment submodule includes a second rotating platform.

7. The fiber laser according to claim 6, characterized in that The first polarization angle adjustment submodule and the second polarization angle adjustment submodule both further include a standard optical fiber ceramic ferrule; The first rotating platform is connected to the dichroic dielectric film via a standard optical fiber ceramic ferrule; The second rotating platform is connected to the semiconductor saturable absorber mirror through a standard optical fiber ceramic ferrule.

8. A laser pulse state tuning method, applied to the fiber laser according to any one of claims 1 to 7, characterized in that: The laser pulse state tuning method comprises: An optical resonant cavity is prepared using polarization-maintaining gain fiber and polarization-maintaining passive fiber; Using a polarization-maintaining single-mode semiconductor pump laser, the pump light passes through a first polarization-maintaining fiber isolator, then through a polarization-maintaining wavelength division multiplexer and a polarization controller, and is input into an optical resonant cavity to obtain an initial mode-locked laser. Tuning the initial mode-locked laser by a tuning method to obtain a mode-locked laser in a target mode-locked state; the tuning method includes a temperature tuning method or an angle tuning method; The mode-locked laser in the target mode-locked state is output through a polarization controller, a polarization-maintaining wavelength division multiplexer, and a second polarization-maintaining optical fiber isolator.

9. The laser pulse state tuning method according to claim 8, characterized in that: When the tuning method is a temperature tuning method, the initial mode-locked laser is tuned by the tuning method to obtain a mode-locked laser in a target mode-locked state, specifically including: determining a target temperature range of the optical resonant cavity based on the mode-locked laser in the target mode-locked state; Lowering the current temperature of the optical resonant cavity to a target temperature by using a semiconductor refrigeration sheet, or raising the current temperature of the optical resonant cavity to a target temperature by using a thin film heating resistor; the target temperature is any temperature within a target temperature range; Use the following formula to calculate the birefringence of the first polarization-maintaining fiber: ΔT = T0 - T; Among them, B T represents the birefringence coefficient of the first polarization-maintaining fiber; C(λ) represents the photoelastic coefficient; E represents Young's modulus; γ represents Poisson's ratio; ε represents the core ellipticity; Δα represents the difference between the linear expansion coefficient of the cladding and the linear expansion coefficient of the stress axis; ΔT represents the temperature difference; T0 represents the melting temperature of the fiber; T represents the target temperature; The propagation constant difference of the first orthogonal polarization component is calculated based on the birefringence coefficient of the first polarization-maintaining fiber using the following formula: Among them, Δβ T represents the propagation constant difference of the first orthogonal polarization component; λ is the mode-locked laser wavelength in the current mode-locked state; Determining whether the propagation constant difference of the first orthogonal polarization component is within a first preset propagation constant difference range, and obtaining a determination result; If the judgment result is yes, a mode-locked laser in the target mode-locked state is obtained; If the judgment result is no, the target temperature is adjusted and the process returns to step "lowering the current temperature of the optical resonant cavity to the target temperature through the semiconductor refrigeration plate, or raising the current temperature of the optical resonant cavity to the target temperature through the thin film heating resistor".

10. The laser pulse state tuning method according to claim 8, characterized in that: When the tuning method is an angle tuning method, the initial mode-locked laser is tuned by the tuning method to obtain a mode-locked laser in a target mode-locked state, specifically including: determining a target polarization angle range of the optical resonant cavity according to the mode-locked laser in the target mode-locked state; The current polarization angle is adjusted to the target polarization angle by the first rotating platform and the second rotating platform to obtain a mode-locked laser in a target mode-locked state; the target polarization angle is any polarization angle within the target polarization angle range.

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