A tunable saddle-shaped spectrum generation device and method

Abstract

This invention discloses a tunable saddle-shaped spectrum generation device and method, belonging to the field of precision machining. It includes: a pump source, a resonant cavity with overall positive dispersion, a mode-locking device, a dispersion management device, and a spectral adjustment component. The pump source excites a gain fiber to generate laser light. The mode-locking device outputs a mode-locked pulse, and the dispersion management device provides positive dispersion. Working in conjunction with the nonlinear effect of self-phase modulation within the cavity, the mode-locked pulse spectrum is directly shaped into a saddle-shaped spectrum with a central depression. The spectral adjustment component achieves flexible tuning of the center wavelength and bandwidth of the output spectrum by adjusting the relative positions of the diffraction grating and the fiber collimator. This invention actively generates a tunable saddle-shaped spectrum from the source, eliminating the need for complex modulation elements in the amplification link. It allows for precise pre-compensation of the gain characteristics of subsequent amplifiers, effectively suppressing gain narrowing effects. It has the advantages of compact structure, low cost, high stability, and high energy utilization.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of precision machining, and particularly relates to a tunable saddle-shaped spectrum generation device and method. BACKGROUND

[0002] With the wide application of femtosecond laser technology in the fields of precision machining, medical diagnosis and treatment, and frontier science, the requirements for pulse width, peak power and beam quality are increasingly improved. At present, the chirped pulse amplification technology is generally used in industrial-grade femtosecond fiber lasers to achieve high-power output. However, in the process of fiber amplification, the inherent gain spectrum characteristics of the gain medium will cause spectral narrowing effect, that is, the pulse spectrum is significantly compressed after amplification, which severely limits the further compression ability of the output pulse and the improvement of the peak power. Therefore, how to effectively suppress the gain narrowing effect has become a key research direction for performance breakthrough of femtosecond fiber lasers.

[0003] In view of the above gain narrowing problem, various suppression schemes have been proposed in the prior art. For example, the spectral pre-shaping technology reshapes the seed spectrum through active elements such as spatial light modulators to compensate for the gain distortion in the amplification process, but this method is complex, costly and unstable. The optimization of the gain medium scheme develops new type of wide-spectrum doped fiber or multi-stage gain fiber splicing to expand the gain bandwidth, but there are limitations such as difficulty in material preparation, increase in nonlinear effects and complex system design. In summary, the existing suppression technologies cannot balance the system simplicity, cost, energy efficiency and stability, and a new type of technology scheme is needed to actively suppress the gain narrowing from the source and has high efficiency and compact structure. SUMMARY

[0004] To solve the above technical problems, the present application provides a tunable saddle-shaped spectrum generation device, comprising: a pump source for generating pump light; a resonant cavity, the overall dispersion in the resonant cavity is all positive dispersion, and the resonant cavity comprises a gain fiber for generating laser under the pumping of the pump light; a mode-locked device arranged in the resonant cavity for realizing mode-locked pulse output; a dispersion management device arranged in the resonant cavity for providing positive dispersion to cooperate with the nonlinear effect to shape the spectrum of the mode-locked pulse into a saddle-shaped spectrum with a central depression; a spectrum adjustment assembly arranged in the resonant cavity for adjusting the central wavelength and spectral bandwidth of the saddle-shaped spectrum.

[0005] Optionally, the resonant cavity is a linear all-fiber resonant cavity, which further comprises a wavelength division multiplexer, and the pump source is coupled with the gain fiber through the wavelength division multiplexer for guiding the pump light into the gain fiber.

[0006] Optionally, the gain fiber is a rare-earth-doped fiber, including ytterbium-doped fiber, erbium-doped fiber, thulium-doped fiber, or bismuth-doped fiber.

[0007] Optionally, the mode-locking device is a saturable absorber, including a semiconductor saturable absorber mirror, carbon nanotubes, or graphene.

[0008] Optionally, the dispersion management device is a chirped fiber grating, used to provide positive dispersion and simultaneously serve as an output coupler to output the saddle-shaped spectrum.

[0009] Optionally, the spectral conditioning component includes: The first fiber collimator is used to convert the laser transmitted through the fiber in the resonant cavity into a spatial beam. A diffraction grating is used to diffract and disperse the spatial beam; and The second fiber collimator is used to receive a portion of the spectrum after it has been split by the diffraction grating, and to recouple it into the fiber for transmission to the mode-locking device.

[0010] Optionally, by adjusting the vertical distance between the second fiber collimator and the diffraction grating, the spectral width received by the second fiber collimator is changed, thereby adjusting the bandwidth of the output saddle-shaped spectrum.

[0011] Optionally, by adjusting the relative horizontal position between the second fiber collimator and the diffraction grating, the center wavelength of the spectrum received by the second fiber collimator is changed, thereby adjusting the center wavelength of the output saddle-shaped spectrum.

[0012] Optionally, the spectral adjustment component includes an acousto-optic tunable filter or a wavelength selection element, used to replace the diffraction grating to achieve spectral adjustment.

[0013] To address the aforementioned technical problems, this invention provides a method for generating a tunable saddle-shaped spectrum, comprising: The pump source provides pump light into the resonant cavity, which has a total positive dispersion, to excite the gain fiber to generate laser light. Mode-lock pulse output is achieved through a mode-locking device; By utilizing the interaction between the positive dispersion and nonlinear effects provided by the dispersion management device, the spectrum of the mode-locked pulse is shaped into a saddle-shaped spectrum with a central depression. By adjusting the spectral tuning components within the resonant cavity, the center wavelength and spectral bandwidth of the saddle-shaped spectrum are tuned, and the tuned saddle-shaped spectrum is output.

[0014] On the other hand, the present invention also provides an electronic device including a memory, a processor, and a computing program stored in the memory and executable on the processor, wherein the processor implements the method when executing the computing program.

[0015] On the other hand, the present invention also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the method.

[0016] Compared with the prior art, the present invention has the following advantages and technical effects: This invention provides a novel solution for actively suppressing gain narrowing at the source of the light source. First, this invention eliminates the need for any active modulation elements or complex feedback systems in the amplification chain, fundamentally avoiding the high cost, complex structure, and poor stability of existing spectral pre-shaping techniques, making it suitable for high-power amplification systems. Second, this invention utilizes an all-fiber linear resonant cavity structure, leveraging the synergistic effect of nonlinearity and positive dispersion to directly output a saddle-shaped spectrum, eliminating the need for special design or splicing of the gain medium, thus reducing system complexity and fabrication difficulty. Finally, the center wavelength and bandwidth of the spectrum generated by this invention can be flexibly tuned, precisely matching the gain characteristics of different amplifiers, achieving efficient compensation for gain narrowing, significantly improving energy utilization and pulse compression quality, and combining the advantages of compact structure, low cost, and stable output. Attached Figure Description

[0017] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a schematic diagram of the structure of the all-fiber mode-locked laser according to an embodiment of the present invention; Figure 2 This is a schematic diagram illustrating spectral tuning achieved by adjusting the relative position of the collimator and the grating according to an embodiment of the present invention; Among them, 1. Pump source, 2. Wavelength division multiplexer, 3. Gain fiber, 4. First fiber collimator, 5. Diffraction grating, 6. Second fiber collimator, 7. Semiconductor saturable absorber mirror, 8. Chirped fiber grating. Detailed Implementation

[0018] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0019] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0020] Example 1 This embodiment provides a tunable saddle-shaped spectrum generation device, comprising: Pump source 1, as a light source that provides energy, is used to generate and output pump light; The wavelength division multiplexer 2 has its reflective end connected to the output pigtail of the pump source 1, and is used to couple the pump light into the subsequent optical path. Gain fiber 3, one end of which is connected to the common end of wavelength division multiplexer 2, is used to absorb pump light to achieve population inversion and serves as the gain medium for laser generation and amplification. The chirped fiber grating 8 has its input end connected to the transmission end of the wavelength division multiplexer 2. It is used to provide positive dispersion for the resonant cavity for dispersion management and also serves as an output coupler. Its transmission end is used to output laser light. The first fiber collimator 4 has its input end connected to the other end of the gain fiber 3, and is used to convert the laser transmitted in the fiber into a collimated spatial beam. The diffraction grating 5 is optically coupled to the output optical path of the first fiber collimator 4 in space, and is used to diffract and split the incident spatial beam to achieve adjustment of the laser center wavelength and spectral bandwidth. The second fiber collimator 6 is spatially optically coupled to the diffraction path of the diffraction grating 5, and is used to receive a portion of the diffracted spectral components and recouple them into the fiber; and The semiconductor saturable absorber mirror 7 is connected to the pigtail of the second fiber collimator 6 to realize and stabilize the passive mode-locking operation of the laser to obtain a mode-locked laser pulse.

[0021] Specifically, in this embodiment, the pump source 1 is installed in a circuit with a temperature control module, and its output pump light has a wavelength of 976 nm, adjustable power, and good stability. The pump light is coupled into the gain fiber 3 via the wavelength division multiplexer 2. The gain fiber 3 is a ytterbium-doped gain fiber with a length of 1 m, which can effectively absorb the 976 nm pump light, causing ytterbium ions to transition from the ground state energy level to a higher energy level, achieving population inversion, and generating laser light in the 1064 nm band. The semiconductor saturable absorber mirror 7 and the chirped fiber grating 8 together constitute a linear resonant cavity for the 1064 nm laser. The chirped fiber grating 8 has a reflectivity greater than 10% and a second-order dispersion value β2 = 0.1 ps², which can provide positive dispersion within the cavity.

[0022] In this embodiment, the line density of the diffraction grating 5 is 1739 lines / mm. By adjusting the angle at which the laser is incident on the diffraction grating 5 to 67°, the diffraction efficiency can be maximized, resulting in the most intense diffracted light. By adjusting the spatial position of the second fiber collimator 6, diffracted light with a specific spectral width can be received. This portion of the light is transmitted via a pigtail to the semiconductor saturable absorber mirror 7, reflected back to the resonant cavity, and finally output as laser light from the transmission end of the chirped fiber grating 8.

[0023] In this embodiment, the formation mechanism of the saddle-shaped spectrum is as follows: When the laser pulse propagates within the cavity, it first undergoes a self-phase modulation effect. Due to the optical Kerr effect, the instantaneous pulse intensity causes an instantaneous change in the refractive index of the optical fiber, and the relationship between these changes is as follows: ; in, It is the instantaneous intensity of the pulse. It is a nonlinear refractive index coefficient. This time-varying refractive index causes a time-varying phase shift in the pulse: ; Where L is the length of action.

[0024] This time-varying phase means that the instantaneous frequency of the pulse is also changing. ; At the leading edge of the pulse, ,therefore This means that the frequency of the pulse leading edge will decrease. At the trailing edge of the pulse, ,therefore This means the frequency of the pulse trailing edge will increase. Therefore, a chirp-free Gaussian pulse, after passing through an SPM (Spectrophotometer), will become a positively chirped pulse with a frequency that changes linearly from red to blue. This positively chirped pulse then enters the positively dispersive medium. In the positively dispersive medium, low-frequency light propagates quickly, while high-frequency light propagates slowly. This speed difference causes the pulse to be broadened in the time domain.

[0025] After the combined effects of SPM and positive dispersion, due to the strong nonlinear interaction and rapid chirp reversal, the time-domain waveform of the pulse may exhibit a slight "dipping" effect. According to the basic principles of Fourier transform, the amplitude modulation in the time domain is directly reflected in the frequency domain. After Fourier transform, this is precisely manifested in the frequency domain as the absence of the center frequency component, forming a saddle-shaped spectrum with a central dip.

[0026] In this embodiment, the output saddle-shaped spectrum can be tuned by adjusting the relative position between the second fiber collimator 6 and the diffraction grating 5. Figure 2As shown, when the vertical distance d between the second fiber collimator 6 and the diffraction grating 5 is changed, the spectral width entering the second fiber collimator 6 changes accordingly: when d increases, the received spectrum narrows; when d decreases, the received spectrum widens, thereby adjusting the output spectral bandwidth. When the horizontal relative position x between the second fiber collimator 6 and the diffraction grating 5 is changed, the center wavelength of the spectrum entering the second fiber collimator 6 shifts accordingly, thereby adjusting the center wavelength of the output spectrum.

[0027] In summary, the tunable saddle-shaped spectrum generation device described in this embodiment directly outputs a centrally concave saddle-shaped spectrum through the synergistic effect of intracavity self-phase modulation and positive dispersion. Furthermore, it utilizes the spatial coupling structure of the diffraction grating and the fiber collimator to achieve flexible tuning of the spectral center wavelength and bandwidth. This allows for pre-compensation of the gain characteristics of the subsequent amplifier, thereby effectively suppressing the gain narrowing effect.

[0028] On the other hand, this embodiment also provides an electronic device, including a memory, a processor, and a computing program stored in the memory and executable on the processor, wherein the processor implements the method when executing the computing program.

[0029] On the other hand, this embodiment also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the method.

[0030] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A device for generating a tunable saddle-shaped spectrum, characterized in that, include: Pump source, used to generate pump light; The resonant cavity has a total positive dispersion and includes a gain fiber for generating laser light under the pump light. A mode-locking device is disposed within the resonant cavity to achieve mode-locked pulse output; A dispersion management device is disposed in the resonant cavity to provide positive dispersion in conjunction with nonlinear effects, so that the spectrum of the mode-locked pulse is shaped into a saddle-shaped spectrum with a central depression. A spectral adjustment component, disposed within the resonant cavity, is used to adjust the center wavelength and spectral bandwidth of the saddle-shaped spectrum.

2. The apparatus according to claim 1, characterized in that, The resonant cavity is a linear all-fiber resonant cavity, which also includes a wavelength division multiplexer. The pump source is coupled to the gain fiber through the wavelength division multiplexer to guide the pump light into the gain fiber.

3. The apparatus according to claim 2, characterized in that, The gain fiber is a rare-earth-doped fiber, including ytterbium-doped fiber, erbium-doped fiber, thulium-doped fiber, or bismuth-doped fiber.

4. The apparatus according to claim 1, characterized in that, The mode-locking device is a saturable absorber, including a semiconductor saturable absorber mirror, carbon nanotubes, or graphene.

5. The apparatus according to claim 1, characterized in that, The dispersion management device is a chirped fiber grating, used to provide positive dispersion and simultaneously act as an output coupler to output the saddle-shaped spectrum.

6. The apparatus according to claim 1, characterized in that, The spectral conditioning component includes: The first fiber collimator is used to convert the laser transmitted through the fiber in the resonant cavity into a spatial beam. A diffraction grating is used to diffract and disperse the spatial beam; and The second fiber collimator is used to receive a portion of the spectrum after it has been split by the diffraction grating, and to recouple it into the fiber for transmission to the mode-locking device.

7. The apparatus according to claim 6, characterized in that, By adjusting the vertical distance between the second fiber collimator and the diffraction grating, the spectral width received by the second fiber collimator is changed, thereby adjusting the bandwidth of the output saddle-shaped spectrum.

8. The apparatus according to claim 6, characterized in that, By adjusting the relative horizontal position between the second fiber collimator and the diffraction grating, the center wavelength of the spectrum received by the second fiber collimator is changed, thereby adjusting the center wavelength of the output saddle-shaped spectrum.

9. The apparatus according to claim 1, characterized in that, The spectral adjustment component includes an acousto-optic tunable filter or wavelength selection element, used to replace the diffraction grating to achieve spectral adjustment.

10. A method for generating a tunable saddle-shaped spectrum, applied to the apparatus according to any one of claims 1 to 9, characterized in that, Includes the following steps: The pump source provides pump light into the resonant cavity, which has a total positive dispersion, to excite the gain fiber to generate laser light. Mode-lock pulse output is achieved through a mode-locking device; By utilizing the interaction between the positive dispersion and nonlinear effects provided by the dispersion management device, the spectrum of the mode-locked pulse is shaped into a saddle-shaped spectrum with a central depression. By adjusting the spectral tuning components within the resonant cavity, the center wavelength and spectral bandwidth of the saddle-shaped spectrum are tuned, and the tuned saddle-shaped spectrum is output.

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