Fiber laser with adjustable repetition frequency

Abstract

The invention relates to the technical field of laser control, in particular to a repetition frequency adjustable fiber laser which comprises a mode-locked laser light path and a spatial light path adjusting module, the spatial light path adjusting module is arranged in the mode-locked laser light path, and the spatial light path adjusting module comprises a piezoelectric ceramic assembly and an electro-optical modulator assembly. The piezoelectric ceramic assembly and the electro-optical modulator assembly achieve locking of the repetition frequency of the fiber laser through voltage cooperative adjustment, the repetition frequency is adjusted from the two dimensions of the physical cavity length and the equivalent cavity length, the fiber laser outputs laser meeting the preset repetition frequency, the all-fiber structure of a linear part is kept, and the optical fiber laser has the advantages of being simple in structure and convenient to use. According to the invention, the device is simple in structure, retains the functions of filtering and dispersion compensation, improves the spectral purity, pulse stability and locking precision of the output laser, avoids the additional loss and polarization disturbance, reduces the overall size of the laser, and covers the frequency demands of different scenes under high precision and wide range.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser control, in particular to a fiber laser with adjustable repetition frequency. BACKGROUND

[0002] The fiber laser has become a core light source in the fields of precision manufacturing, biological imaging, optical communication, etc. due to its ultra-short pulse output characteristics. The repetition frequency of the output laser directly determines the time interval of the pulse sequence and is a key parameter affecting the application accuracy. Since the repetition frequency is inversely proportional to the cavity length, the current industry focuses on controlling the equivalent cavity length of the laser resonant cavity to adjust the repetition frequency. However, in order to optimize the laser output quality, such as filtering and dispersion compensation, the existing technology usually uses chirped fiber gratings, uniform fiber Bragg gratings, etc. as reflective elements. These elements need to be set at the end of the linear part of the ring mode-locked laser light path through fiber fusion to maintain the all-fiber structure of the linear part and avoid additional optical path loss and polarization disturbance.

[0003] In the existing technology, the spatial optical path adjustment module for adjusting the repetition frequency of the fiber laser is generally set at the end of the linear part on the same side as the reflective element. This design destroys the all-fiber structure of the linear part, limits the types of reflective elements, and cannot simultaneously achieve the adjustment of the repetition frequency and the optimization of the laser output quality using reflective elements, such as filtering and dispersion compensation. If a full-fiber adjustment module is forcibly used, there are problems of low adjustment accuracy and difficulty in cooperation with electro-optical modulators, resulting in a conflict between structure adaptation and function realization. At the same time, the existing spatial optical path adjustment module is connected to the port of the ring light path as an external accessory, rather than being set inside the ring, which leads to a relatively large overall volume of the light path, is not conducive to miniaturization applications, and the connection part of the spatial optical path adjustment module and the ring light path is exposed to the external environment, which is easily affected by dust and temperature fluctuations, introducing additional optical path loss and frequency drift, thereby reducing the long-term stable operation ability of the laser and increasing the maintenance cost.

[0004] Therefore, how to simultaneously consider the adaptability of the all-fiber structure of the linear part to the reflective filtering module and improve the integration of the spatial optical path adjustment module and the ring light path to enhance the environmental anti-interference ability in the fiber laser with adjustable repetition frequency has become a problem to be solved. SUMMARY

[0005] To solve the above technical problems, the technical solution adopted by the present application is a fiber laser with adjustable repetition frequency, which comprises a mode-locked laser light path and a spatial optical path adjustment module. The spatial light path adjustment module is arranged inside the mode-locked laser light path, and comprises a piezoelectric ceramic component and an electro-optical modulator component.

[0006] In some embodiments, the mode-locked laser light path is a ring mode-locked laser light path, and the fiber laser further comprises a reflective filtering module. The ring mode-locked laser light path forms a closed laser transmission path, and the reflective filtering module is arranged at the tail end of the linear part of the ring mode-locked laser light path. The spatial light path adjustment module is arranged inside the ring mode-locked laser light path, and comprises a piezoelectric ceramic component and an electro-optical modulator component.

[0007] In some embodiments, the ring mode-locked laser light path comprises at least a wavelength division multiplexer, a gain fiber, a first fiber coupler, a fiber phase shifter and a second fiber coupler, and the components in the ring mode-locked laser light path are sequentially connected by fibers to form a loop structure.

[0008] In some embodiments, the ring mode-locked laser light path further comprises a pump laser, wherein the output end of the pump laser is connected to the input end of the wavelength division multiplexer, and the pump laser is used to provide pump light to the gain fiber.

[0009] In some embodiments, the input end of the spatial light path adjustment module is connected to the output end of the first fiber coupler, and the output end of the spatial light path adjustment module is connected to the input end of the fiber phase shifter.

[0010] In some embodiments, the reflective filtering module is a chirped fiber grating, and the reflective filtering module is connected to the output end of the second fiber coupler. The reflective filtering module is used to realize laser reflection, limit laser central wavelength and spectral width, and compensate for the dispersion of other fibers in the ring mode-locked laser light path.

[0011] In some embodiments, the fiber laser further comprises a first output isolator and an optoelectronic converter, the input end of the first output isolator is connected to the branch output end of the second fiber coupler, and the output end of the first output isolator is connected to the input end of the optoelectronic converter. The first output isolator is used to prevent external reflected light from entering the ring-shaped mode-locked laser light path, and the photoelectric converter is used to convert a laser signal into an electric signal to detect a repetition frequency.

[0012] In some embodiments, the fiber laser further comprises a servo control system electrically connected with the piezoelectric ceramic component, the electro-optical modulator component and the photoelectric converter respectively. The servo control system is used to obtain the laser repetition frequency detected by the photoelectric converter, control the voltage applied to the piezoelectric ceramic component to make the laser repetition frequency fall within a first preset frequency range, and control the voltage applied to the electro-optical modulator component to stabilize the laser repetition frequency within a second preset frequency range, wherein the first preset frequency range and the second preset frequency range have a preset repetition frequency as a center value, and the second preset frequency range is smaller than the first preset frequency range.

[0013] In some embodiments, the servo control system comprises a microprocessor, a D / A conversion module and a signal acquisition module. The signal acquisition module and the photoelectric converter are electrically connected, used to acquire the electric signal output by the photoelectric converter and convert it into a digital signal transmitted to the microprocessor. The microprocessor is used to output voltage control signals to the piezoelectric ceramic component and the electro-optical modulator component through the D / A conversion module according to the difference between the digital signal and the first preset frequency range and the second preset frequency range.

[0014] In some embodiments, the spatial light path adjustment module further comprises a first collimator and a second collimator, wherein the first collimator and the piezoelectric ceramic component are fixed as a whole, the first collimator converts the transmission mode of the laser inside the ring-shaped mode-locked laser light path from fiber transmission to spatial transmission, and the second collimator is fixed as a whole with the electro-optical modulator component through an adapter, the second collimator converts the transmission mode from the spatial transmission mode to the fiber transmission mode again.

[0015] The application also provides a laser output method applied to the fiber mode-locked laser as described in any one of the above embodiments, and the method comprises: obtaining a preset repetition frequency, a first preset frequency range and a second preset frequency range, wherein the first preset frequency range and the second preset frequency range have the preset repetition frequency as a center value, and the second preset frequency range is smaller than the first preset frequency range; acquiring the laser repetition frequency of the fiber laser; By comparing the laser repetition frequency with the first preset frequency range and the second preset frequency range, the voltage applied to the piezoelectric ceramic component and the electro-optic modulator component is controlled to obtain output laser meeting the preset repetition frequency.

[0016] In some embodiments, the control of the voltage applied to the piezoelectric ceramic component and the electro-optic modulator component by comparing the laser repetition frequency with the first preset frequency range and the second preset frequency range to obtain output laser meeting the preset repetition frequency comprises: comparing the laser repetition frequency with the first preset frequency range to obtain a first comparison result; If the first comparison result is that the laser repetition frequency is within the first preset frequency range, then the laser repetition frequency signal is compared with the second preset frequency range to obtain a second comparison result, otherwise, the voltage applied to the piezoelectric ceramic component is controlled to change the physical cavity length of the piezoelectric ceramic component, thereby adjusting the laser repetition frequency, and repeating the comparison of the laser repetition frequency with the first preset frequency range until the first comparison result is that the laser repetition frequency is within the first preset frequency range; If the second comparison result is that the laser repetition frequency is within the second preset frequency range, then output laser meeting the preset repetition frequency is obtained, otherwise, the voltage applied to the electro-optic modulator component is controlled to change the internal refractive index of the electro-optic modulator component, thereby adjusting the laser repetition frequency, and repeating the comparison of the repetition frequency with the second preset frequency range until the second comparison result is that the repetition frequency is within the second preset frequency range.

[0017] Compared with the prior art, the present application has at least the following beneficial effects: by arranging the spatial light path adjustment module inside the mode-locked laser light path, the spatial light path adjustment module includes a piezoelectric ceramic component and an electro-optic modulator component, the piezoelectric ceramic component and the electro-optic modulator component are cooperatively adjusted by voltage to realize the locking of the repetition frequency of the fiber laser, the repetition frequency is adjusted from two dimensions of physical cavity length and equivalent cavity length, the output of the fiber laser meets the preset repetition frequency of the laser, the linear part maintains the all-fiber structure, the filtering and dispersion compensation function is retained, the spectral purity, pulse stability and locking accuracy of the output laser are improved, additional loss and polarization disturbance are avoided, the overall volume of the laser is reduced, and the frequency requirements of different scenes under high precision and wide range are covered. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort.

[0019] Figure 1 A structural schematic diagram of a fiber laser provided by the embodiments of the present application is shown in FIG. 1. Figure 2 Another structural schematic diagram of a fiber laser provided by the embodiments of the present application is shown in FIG. 2. In the drawings, 1 is a mode-locked laser light path, 10 is a ring mode-locked laser light path, 11 is a wavelength division multiplexer, 12 is a gain fiber, 13 is a first fiber coupler, 14 is a fiber phase shifter, 15 is a second fiber coupler, 16 is a pump laser, 2 is a spatial light path adjustment module, 21 is a piezoelectric ceramic component, 22 is an electro-optical modulator component, 23 is a first collimator, 24 is a second collimator, 3 is a reflection filter module, 4 is a first output isolator, 5 is an optoelectronic converter, and 6 is a servo control system. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without any creative effort belong to the scope of protection of the present application.

[0021] It should be noted that the terms "first", "second", and the like in the specification and claims of the present application and the above-described drawings are used to distinguish similar objects, and do not necessarily indicate a specific order or sequence. It can be understood that the above-described terms for distinguishing similar objects can be interchanged under appropriate circumstances, so that the present application can also implement other embodiments in addition to the above-described illustrated embodiments or described embodiments. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or server including a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to the process, method, product, or device.

[0022] The embodiments of the present application provide a fiber laser with adjustable repetition frequency. In some embodiments, as shown in FIG. 1, the fiber laser includes a mode-locked laser light path 1 and a spatial light path adjustment module 2. Figure 1 ​The spatial optical path adjustment module 2 is located inside the mode-locked laser optical path 1. The spatial optical path adjustment module 2 includes a piezoelectric ceramic component 21 and an electro-optic modulator component 22. The piezoelectric ceramic component 21 and the electro-optic modulator component 22 lock the repetition frequency of the fiber laser through voltage coordinated adjustment, so that the fiber laser outputs laser that conforms to the preset repetition frequency.

[0023] In some embodiments, such as Figure 2 As shown, the mode-locked laser optical path 1 is a ring-shaped mode-locked laser optical path 10, and the spatial optical path adjustment module 2 also includes a reflection filtering module 3.

[0024] The annular mode-locked laser optical path 10 forms a closed laser transmission path, and the reflection filter module 3 is located at the end of the linear section of the annular mode-locked laser optical path 10.

[0025] Among them, the annular mode-locked laser optical path 10 and the reflection filter module 3 are used to form a mode-locked pulse sequence with extremely narrow pulse width (usually picosecond to femtosecond level) and stable repetition frequency.

[0026] The spatial optical path adjustment module 2 is located inside the loop of the annular mode-locked laser optical path 10. Through the synergistic effect of the piezoelectric ceramic component 21 and the electro-optic modulator component 22, the repetition frequency is adjusted from two dimensions: "physical cavity length" and "equivalent cavity length".

[0027] Specifically, when an adjustable voltage (e.g., 0V-150V) is applied to the piezoelectric ceramic component 21, the piezoelectric ceramic component 21 will undergo linear deformation along the axial direction (deformation coefficient approximately 100nm / V, e.g., 10μm deformation when 100V is applied), directly changing the physical cavity length of the ring mode-locked laser optical path 10, i.e., the total length of the optical path, thereby adjusting the repetition frequency of the fiber laser. The adjustment range of the piezoelectric ceramic component 21 is typically 40Hz-1.4KHz, which can quickly cover the repetition frequency span required for multiple scenarios. However, it has a low control bandwidth (millisecond-level response), is greatly affected by temperature drift, and its stability can only reach the ±1mHz level. Therefore, it is used for "coarse tuning," that is, quickly pulling the repetition frequency of the output laser into the target range.

[0028] The electro-optic modulator assembly 22 is connected in series in the spatial optical path. When an adjustable voltage (e.g., 0V-120V) is applied to the electro-optic modulator assembly 22, the refractive index of the lithium niobate crystal inside the electro-optic modulator assembly 22 changes, causing a change in the transmission speed of the laser signal within the electro-optic modulator assembly 22. This is equivalent to changing the equivalent cavity length of the ring mode-locked laser optical path 10, which is the effective optical path of the actual laser transmission. The adjustment range of the electro-optic modulator assembly 22 is typically 0.02Hz-1Hz, but it has a high control bandwidth (microsecond-level response), is less susceptible to environmental interference, and has a stability of ±0.1mHz. Therefore, it is used for "fine-tuning," that is, based on the coarse-tuning of the piezoelectric ceramic assembly 21, to precisely lock the repetition frequency of the output laser to a preset value.

[0029] In the above-described manner, the spatial optical path adjustment module 2 is located inside the loop of the annular mode-locked laser optical path 10, and the reflection filter module 3 is located at the end of the linear section. This maintains the all-fiber structure of the linear section while retaining the filtering and dispersion compensation functions, significantly improving the spectral purity and pulse stability of the output laser, avoiding additional losses and polarization disturbances, and reducing the overall size of the laser to adapt to more application scenarios. Through the synergistic effect of the piezoelectric ceramic component 21 and the electro-optic modulator component 22, the repetition frequency is adjusted from two dimensions: physical cavity length and equivalent cavity length. This covers the frequency requirements of different scenarios under high precision and wide range, and also achieves high-precision locking of the repetition frequency.

[0030] In some embodiments, such as Figure 2 As shown, the ring mode-locked laser optical path 10 includes at least a wavelength division multiplexer 11, a gain fiber 12, a first fiber coupler 13, a fiber phase shifter 14, and a second fiber coupler 15. The components in the ring mode-locked laser optical path 10 are connected in sequence through optical fibers to form a ring structure.

[0031] The wavelength division multiplexer 11 is used to achieve co-fiber transmission of the pump light output from the pump laser 16 and the laser signal light transmitted in the ring optical path, so as to avoid mutual interference between the two lights and prevent the signal light from flowing back into the pump laser 16 and damaging the device.

[0032] The wavelength division multiplexer 11 can be designed based on the wavelength selective transmission / reflection of light. For example, the pump light wavelength is 976nm (used to excite the gain fiber), and the laser signal light wavelength is 1030nm-1080nm (mode-locked laser output band). The filter film or fiber grating in the wavelength division multiplexer 11 only allows the 976nm pump light to pass through into the gain fiber, while allowing the 1030-1080nm signal light to propagate forward along the ring optical path. The reverse signal light is isolated (isolation degree ≥30dB) to ensure the unidirectionality of the optical path.

[0033] Gain fiber 12 is used to absorb pump light energy, amplifying low-energy spontaneous emission light into high-energy stimulated emission light, providing continuous laser gain for the ring optical path, and satisfying the threshold condition that the gain of laser oscillation is greater than the loss. Taking the commonly used ytterbium-doped gain fiber as an example, the fiber core is doped with ytterbium ions. When irradiated by 976nm pump light, the ytterbium ions are excited from the ground state to the excited state. The excited-state ions are unstable and will transition back to the ground state through stimulated emission, releasing photons in the 1030nm-1080nm band (with the same wavelength and phase as the incident signal light), realizing exponential amplification of the signal light. At the same time, the length of the gain fiber (usually 1m-5m) and the doping concentration (500ppm-1000ppm) need to be matched with the pump power to ensure uniform gain and no significant thermal loss.

[0034] The first fiber coupler 13 is used to split the laser signal amplified by the gain fiber 12 into two paths. One path enters the subsequent spatial optical path adjustment module 2 for repetition frequency adjustment, and the other path serves as the final laser output, used to monitor the optical power / wavelength in the cavity in real time, and realize the function of adjustment and signal output.

[0035] In some embodiments, the first fiber optic coupler 13 has one path leading to the subsequent spatial optical path adjustment module 2, and the other path is equipped with a second output isolator. The second output isolator can prevent backlighting and reduce the probability of device damage.

[0036] The fiber phase shifter 14 is used to periodically change the phase of the laser in the cavity, thereby disrupting the phase randomness of different frequency laser modes, forcing each mode to form a fixed phase difference, and finally superimposing to generate an ultrashort mode-locked pulse sequence instead of a continuous laser.

[0037] The second fiber coupler 15 is used to split the laser signal after it has been processed by the spatial optical path adjustment module 2 and the fiber phase shifter 14 into two paths. One path is reflected back to the ring optical path through the reflection filter module 3 to maintain laser oscillation. The other path can be reserved as a monitoring port for real-time monitoring of the optical power / wavelength / repetition frequency in the cavity, thereby realizing the functions of oscillation maintenance and monitoring.

[0038] The components are connected in series via optical fibers in the following order to form a closed laser transmission path. The specific connection relationship is as follows: signal light output of wavelength division multiplexer 11 → input of gain fiber 12 → output of gain fiber 12 → input of first fiber coupler 13 → main output of first fiber coupler 13 → input of spatial optical path adjustment module 2 → output of spatial optical path adjustment module 2 → input of fiber phase shifter 14 → output of fiber phase shifter 14 → input of second fiber coupler 15 → reflection of second fiber coupler 15 → input of reflection filter module 3 → reflection of reflection filter module 3 → signal light input of wavelength division multiplexer 11.

[0039] In the above manner, the closed loop ensures that the laser signal is continuously transmitted back and forth along a fixed path, and is continuously amplified in the gain fiber 12. At the same time, the loss is controlled by components such as the wavelength division multiplexer 11 and the fiber coupler, and finally the laser oscillation threshold of "gain ≥ total loss" is met, forming a stable laser signal. Meanwhile, the periodic phase modulation of the fiber phase shifter 14 can be applied to the laser signal in each round of transmission, continuously screening the phase-matching mode and avoiding pulse distortion caused by mode competition. At the same time, the reflected light from the reflection filter module 3 can be accurately transmitted back to the wavelength division multiplexer 11, ensuring the stability of the optical path and further improving the temporal stability of the mode-locked pulse. Furthermore, the closed loop incorporates the spatial optical path adjustment module 2 into the core transmission path, so that the adjustment effect of the piezoelectric ceramic component 21 changing the physical cavity length and the electro-optic modulator component 22 changing the equivalent cavity length can directly affect the total optical path of the entire loop, thereby accurately controlling the repetition frequency and preventing the adjustment effect from being bypassed or weakened.

[0040] In some embodiments, the gain fiber can be at least one or more of ytterbium-doped fiber, erbium-doped fiber, erbium-ytterbium co-doped fiber, and neodymium-doped fiber, with corresponding signal wavelength ranges of 1030nm-1080nm, 1530nm-1565nm, 1530nm-1565nm, and 1064nm-1319nm, respectively.

[0041] In some embodiments, the fiber optic phase shifter 14 includes at least one or more of the following: piezoelectric fiber optic phase shifter, photoelectric fiber optic phase shifter, temperature-controlled fiber optic phase shifter, and magneto-optic fiber optic phase shifter.

[0042] In some embodiments, the components in the annular mode-locked laser optical path 10 can be connected in series using at least one or more types of optical fibers, such as polarization-maintaining fiber, single-mode fiber, double-clad fiber, and dispersion-compensating fiber.

[0043] In some embodiments, such as Figure 2 As shown, the ring mode-locked laser optical path 10 also includes a pump laser 16, wherein the output end of the pump laser 16 is connected to the input end of the wavelength division multiplexer 11, and is used to provide pump light to the gain fiber 12.

[0044] The output wavelength of the pump laser 16 is strictly matched with the absorption wavelength of the gain fiber 12. For example, the ytterbium-doped gain fiber 12 needs to be paired with a pump laser with a wavelength of 976nm or 915nm, and the erbium-doped gain fiber 12 needs to be paired with a pump laser with a wavelength of 980nm or 1480nm, so as to ensure that the gain fiber 12 can efficiently absorb the pump light energy.

[0045] In some embodiments, the input end of the spatial optical path adjustment module 2 is connected to the output end of the first optical fiber coupler 13, and the output end of the spatial optical path adjustment module 2 is connected to the input end of the optical fiber phase shifter 14.

[0046] In some embodiments, the reflection filter module 3 is a chirped fiber grating, and the reflection filter module 3 is connected to the output end of the second fiber coupler 15.

[0047] Among them, the reflection filtering module 3 is used to realize laser reflection, limit the center wavelength and spectral width of the laser, and compensate for the dispersion of other optical fibers in the ring mode-locked laser optical path 10.

[0048] The input end of the chirped fiber grating is connected to the reflective end of the second fiber coupler 15 via fiber fusion splicing. The second fiber coupler 15 typically uses a coupling ratio of 80:20, where 80% of the signal light (oscillation path) is transmitted to the chirped fiber grating, reflected, and then transmitted back to the ring optical path, while 20% of the signal light (output path) is output externally, ensuring that the light intensity of the oscillation path is sufficient to maintain the laser cycle.

[0049] Specifically, the chirped fiber grating, acting as the reflection filter module 3, is based on the Bragg reflection principle. That is, there is periodic refractive index modulation within the core of the chirped fiber grating. Only signal light satisfying the Bragg condition is strongly reflected, while stray light not satisfying the Bragg condition is transmitted or lost. The reflected signal light returns along the original path to the loop optical path, continuously participating in oscillation and ensuring uninterrupted laser circulation in the closed optical path. Simultaneously, the reflection wavelength range of the chirped fiber grating is determined by the grating pitch variation range (e.g., a grating pitch of 1050nm-1100nm corresponds to a reflection wavelength of 1030-1080nm), which can precisely limit the center wavelength and spectral width of the laser, filtering out spontaneous emission stray light generated by the gain fiber 12 and improving the spectral purity of the output laser. Meanwhile, the gain fiber 12 and transmission fiber in the ring optical path will generate "positive dispersion" which will cause the ultrashort pulse to broaden. The chirped structure of the chirped fiber grating can generate "negative dispersion". The dispersion compensation is -500ps / nm to -1000ps / nm. By matching the amount of negative dispersion with the total amount of positive dispersion in the cavity, the pulse broadening effect can be canceled, ensuring that the mode-locked pulse maintains narrow pulse characteristics during transmission.

[0050] In some embodiments, the chirped fiber grating can be at least one or more of the following types: polarization-maintaining chirped fiber grating, non-polarization-maintaining broadband chirped fiber grating, and high-reflectivity chirped fiber grating.

[0051] In the above method, by using fiber optic fusion splicing, it is ensured that the linear section tail end can maintain an all-fiber structure, avoiding the splicing difficulties and additional losses caused by setting the spatial optical path at the end of the linear section in the prior art, while ensuring that the filtering and dispersion compensation functions of the chirped fiber grating are functioning normally.

[0052] In some embodiments, such as Figure 2As shown, the fiber laser also includes a first output isolator 4 and a photoelectric converter 5. The input end of the first output isolator 4 is connected to the branch output end of the second fiber coupler 15, and the output end of the first output isolator 4 is connected to the input end of the photoelectric converter 5.

[0053] The first output isolator 4 is used to prevent external reflected light from entering the ring mode-locked laser optical path 10, and the photoelectric converter 5 is used to convert the laser signal into an electrical signal to detect the repetition frequency.

[0054] The first output isolator 4 achieves unidirectional light transmission based on the Faraday magneto-optical effect. Specifically, the first output isolator 4 contains components such as a magnetic ring, a Faraday rotator, and a polarizer. When the laser (forward light) output from the branch of the second fiber coupler 15 enters the isolator, the constant magnetic field generated by the magnetic ring causes the Faraday rotator to rotate the polarization state of the laser by 45°. This polarization state is exactly consistent with the light transmission direction of the downstream polarizer, allowing the laser to pass through smoothly. If there is reflected light (reverse light, such as reflection from the optical element at the laser output end) attempting to enter the isolator, the polarization state of the reverse light is rotated by 45° again after passing through the Faraday rotator. At this time, the polarization state is perpendicular to the light transmission direction of the upstream polarizer, and the reverse light is strongly suppressed, preventing it from entering the ring mode-locked laser optical path 10, thereby blocking the transmission of reverse light and extending the service life of the core components.

[0055] The photoelectric converter 5 realizes photoelectric signal conversion based on the photoelectric effect. Specifically, when the photosensitive layer of the photoelectric converter 5 (such as silicon or indium gallium arsenide material) is irradiated by laser, the valence band electrons absorb photon energy and jump to the conduction band to form photogenerated charge carriers. The charge carriers move directionally under the action of the internal electric field, generating a current signal proportional to the incident light power. The photocurrent is then converted into a voltage signal by the internal amplification circuit, and finally outputs an electrical signal synchronized with the laser pulse for the servo control system 6 to detect the repetition frequency.

[0056] In some embodiments, the photoelectric converter 5 can be at least a discrete photoelectric converter, an integrated photoelectric converter, or an array photoelectric converter, and can be selected according to the actual laser size requirements.

[0057] In some embodiments, such as Figure 2 As shown, the fiber laser also includes a servo control system 6, which is electrically connected to the piezoelectric ceramic component 21, the electro-optic modulator component 22, and the photoelectric converter 5.

[0058] The servo control system 6 is used to acquire the laser repetition frequency detected by the photoelectric converter 5. First, it controls the voltage applied to the piezoelectric ceramic component 21 to make the laser repetition frequency fall into the first preset frequency range. Then, it controls the voltage applied to the electro-optic modulator component 22 to stabilize the laser repetition frequency in the second preset frequency range. The first preset frequency range and the second preset frequency range are centered on the preset repetition frequency, and the second preset frequency range is smaller than the first preset frequency range.

[0059] In some embodiments, such as Figure 2 As shown, the servo control system 6 includes a microprocessor, a D / A conversion module, and a signal acquisition module.

[0060] The signal acquisition module is electrically connected to the photoelectric converter 5 and is used to acquire the electrical signal output by the photoelectric converter 5 and convert it into a digital signal for transmission to the microprocessor.

[0061] The microprocessor is used to output voltage control signals to the piezoelectric ceramic component 21 and the electro-optic modulator component 22 respectively through the D / A conversion module based on the difference between the digital signal and the first preset frequency range and the second preset frequency range.

[0062] Among them, the photoelectric converter 5 converts the laser light signal into an electrical signal and transmits it to the signal acquisition module of the servo control system 6; the signal acquisition module has a built-in high-speed ADC chip (such as 16-bit resolution, sampling rate ≥1GS / s) to convert the analog electrical signal into a digital frequency signal and remove spike noise in the signal to ensure data authenticity; the digital frequency signal is transmitted to the microprocessor through the internal data bus (such as SPI, I2C).

[0063] A microprocessor (such as a 32-bit ARM processor) acts as the control center. It compares the current laser repetition frequency with a threshold range by calling preset repetition frequencies (e.g., 80,000,000Hz), a first preset frequency range (e.g., 80,000,000±100Hz), and a second preset frequency range (e.g., 80,000,000±0.02Hz) stored in pre-stored registers. If the laser repetition frequency is less than the lower limit of the first preset frequency range or greater than the upper limit of the first preset frequency range, i.e., it does not fall within the first preset frequency range, the piezoelectric ceramic component 21 is activated in coarse adjustment mode to quickly bring the laser repetition frequency into the first preset frequency range.

[0064] If the laser repetition frequency is within the first preset frequency range but not within the second preset frequency range, the fine-tuning mode of the electro-optic modulator component 22 is activated to precisely lock the laser repetition frequency within the second preset frequency range.

[0065] If the current frequency falls within the second preset frequency range, the current voltage output is maintained, and dynamic monitoring mode is entered. The frequency data can be refreshed according to a preset period to prevent drift. The preset period can be set according to actual needs, such as 1ms, 2ms, etc.

[0066] When controlling the voltage applied to the piezoelectric ceramic component 21, the microprocessor calculates the required coarse adjustment voltage based on the difference between the current laser repetition frequency and the first preset frequency range using the "voltage-frequency mapping algorithm" corresponding to the piezoelectric ceramic component 21. For example, if the laser repetition frequency of 80,000,020Hz differs from the first threshold lower limit of 80,000,050Hz by 30Hz, and the "voltage-frequency adjustment coefficient" of the piezoelectric ceramic component 21 is known to be 3Hz / V (i.e., for every 1V increase in voltage, the frequency increases by 3Hz), then a 10V voltage needs to be output, which is then superimposed on the current voltage of the piezoelectric ceramic component 21 to obtain the target voltage.

[0067] When controlling the voltage applied to the electro-optic modulator component 22, the microprocessor calculates the required fine-tuning voltage based on the difference between the current laser repetition frequency and the second preset frequency range using the "voltage-frequency mapping algorithm" corresponding to the electro-optic modulator component 22. For example, if the current laser repetition frequency of 80,000,000.05Hz differs from the second threshold upper limit of 80,000,000Hz by 0.05Hz, and the "voltage-frequency adjustment coefficient" of the electro-optic modulator component 22 is known to be 5mHz / V (i.e., for every 1V increase in voltage, the frequency decreases by 5mHz), then a 10V voltage needs to be output, and the target voltage is obtained by superimposing the current voltage of the electro-optic modulator component 22.

[0068] Furthermore, the microprocessor transmits the target voltage command to the D / A conversion module, converts it into an analog voltage signal, and applies it to one or more of the piezoelectric ceramic component 21 and the electro-optic modulator component 22.

[0069] In some embodiments, the piezoelectric ceramic component 21 may be at least one or more of the following types: columnar piezoelectric ceramic, multilayer piezoelectric ceramic, etc.

[0070] In some embodiments, the electro-optic modulator component 22 may be at least a lithium niobate polarization-maintaining electro-optic modulator, a non-polarization-maintaining lithium niobate electro-optic modulator, or the like.

[0071] In some embodiments, the preset repetition frequency, the first preset frequency range, and the second preset frequency range can be modified in real time by a host computer (e.g., adjusting the target frequency from 80,000,020Hz to 80,000,050Hz, and changing the first threshold range from ±100Hz to ±200Hz) without hardware modifications, adapting to different repetition frequency requirements.

[0072] In the above manner, the servo control system 6, through closed-loop collaboration with the piezoelectric ceramic component 21, the electro-optic modulator component 22, and the photoelectric converter 5, specifically addresses the problems of low repetition frequency adjustment efficiency, poor accuracy, and weak anti-interference capability in the existing technology. Furthermore, the servo control system 6, through its configurable parameter and switchable mode design, can adapt to different types of fiber lasers and application scenarios, solving the problems of high customization cost and poor compatibility in the existing solutions.

[0073] In some embodiments, such as Figure 2 As shown, the spatial optical path adjustment module 2 also includes a first collimator 23 and a second collimator 24, wherein the first collimator 23 and the piezoelectric ceramic component 21 are fixed together, and the second collimator 24 is fixed together with the electro-optic modulator component 22 through an adapter.

[0074] The first collimator 23 and the piezoelectric ceramic assembly 21 are fixed together by an L-shaped metal bracket. Specifically, a semi-cylindrical slot matching the outer shell of the first collimator 23 is opened on one side of the bracket, and a flange fixing hole matching the moving end of the piezoelectric ceramic assembly 21 is opened on the other side. After locking, the parallelism between the optical axis of the collimator and the deformation direction of the piezoelectric ceramic is calibrated by a laser interferometer to ensure that the collimator moves only along the optical axis when the piezoelectric ceramic expands or contracts.

[0075] The second collimator 24 and the electro-optic modulator assembly 22 are fixed together by an adapter. One side of the adapter has an electro-optic modulator fixing groove that matches the output flange of the electro-optic modulator assembly 22, and the other side has a second collimator slot that matches the housing of the second collimator 24. After locking, the coaxiality between the optical axis of the electro-optic modulator and the slot of the adapter is calibrated.

[0076] The adapter can be made of alloys, plastics, ceramics, or other materials.

[0077] In some embodiments, the first collimator 23 and the second collimator 24 may be at least one or more types such as polarization-maintaining fiber collimators and high-power non-polarization-maintaining collimators.

[0078] In some embodiments, the spatial optical path adjustment module 2 further includes a sealed housing, and the piezoelectric ceramic assembly 21, the electro-optic modulator assembly 22, the first collimator 23, the second collimator 24 and the adapter are all encapsulated inside the sealed housing.

[0079] The inner wall of the sealed housing is provided with a heat insulation layer, and the sealed housing is provided with a sealed interface for the cables of the piezoelectric ceramic component 21 and the electro-optic modulator component 22 to pass through.

[0080] This application also provides a laser output method, applied to a fiber laser as described in any of the foregoing embodiments, for example... Figure 2 The fiber laser shown includes the following laser output methods: Obtain a preset repetition frequency, a first preset frequency range, and a second preset frequency range, wherein the first preset frequency range and the second preset frequency range are centered on the preset repetition frequency, and the second preset frequency range is smaller than the first preset frequency range.

[0081] The laser repetition frequency of the fiber laser is collected.

[0082] By comparing the laser repetition frequency with the first preset frequency range and the second preset frequency range, the voltage applied to the piezoelectric ceramic component 21 and the electro-optic modulator component 22 is controlled to obtain an output laser that conforms to the preset repetition frequency.

[0083] In some implementations, the voltage applied to the piezoelectric ceramic component 21 and the electro-optic modulator component 22 is controlled by comparing the laser repetition frequency with a first preset frequency range and a second preset frequency range to obtain an output laser that conforms to the preset repetition frequency, including: The first comparison result is obtained by comparing the laser repetition frequency with the first preset frequency range.

[0084] If the first comparison result is that the laser repetition frequency is within the first preset frequency range, then the laser repetition frequency signal and the second preset frequency range are compared to obtain the second comparison result. Otherwise, the voltage applied to the piezoelectric ceramic component 21 is controlled to change the physical cavity length of the piezoelectric ceramic component 21, thereby adjusting the laser repetition frequency. The laser repetition frequency and the first preset frequency range are compared repeatedly until the first comparison result is that the laser repetition frequency is within the first preset frequency range.

[0085] If the second comparison result is that the laser repetition frequency is within the second preset frequency range, then an output laser that meets the preset repetition frequency is obtained; otherwise, the voltage applied to the electro-optic modulator component 22 is controlled to change the internal refractive index of the electro-optic modulator component 22, thereby adjusting the laser repetition frequency, and the comparison between the repetition frequency and the second preset frequency range is repeated until the second comparison result is that the repetition frequency is within the second preset frequency range.

[0086] Specifically, by setting a preset repetition frequency, a first range parameter, and a second range parameter, with the second range parameter being smaller than the first range parameter, the difference between the preset repetition frequency and the first range parameter is used as the lower limit of the first preset frequency range, and the sum of the preset repetition frequency and the first range parameter is used as the upper limit of the first preset frequency range; similarly, the difference between the preset repetition frequency and the second range parameter is used as the lower limit of the second preset frequency range, and the sum of the preset repetition frequency and the second range parameter is used as the upper limit of the second preset frequency range. For example, if the preset repetition frequency is 80,000,000Hz, the first range parameter is 100Hz, and the second range parameter is 50mHz, then the first preset frequency range is [79,999,950Hz, 80,000,050Hz], and the second preset frequency range is [79,999,999.975Hz, 80,000,000.025Hz].

[0087] The real-time laser repetition frequency of the fiber laser is acquired by the photoelectric converter 5. By comparison, the microprocessor of the servo control system 6 performs a comparison between the laser repetition frequency and the first preset frequency range, and between the laser repetition frequency and the second preset frequency range, and outputs the first comparison result and the second comparison result.

[0088] The servo control system 6 calculates the required voltage adjustment for the piezoelectric ceramic component 21 / electro-optic modulator component 22 based on the deviation between the laser repetition frequency and the first preset frequency range / second preset frequency range. By controlling the voltage applied to the piezoelectric ceramic component 21, the physical cavity length of the piezoelectric ceramic component 21 is changed, thereby achieving coarse frequency adjustment based on the piezoelectric ceramic component 21, solving the problem of large frequency deviation, and quickly pulling back to a wide frequency range. Furthermore, by controlling the voltage applied to the electro-optic modulator component 22, the internal refractive index of the electro-optic modulator component 22 is changed, thereby adjusting the laser repetition frequency, thereby achieving fine frequency adjustment based on the electro-optic modulator component 22, solving the problem of small frequency deviation, and accurately locking the narrow frequency range.

[0089] As described above, based on the logic of dual-frequency range and dual-component coordinated control, the piezoelectric ceramic component 21 changes the physical cavity length, quickly pulling the repetition frequency that deviates significantly back to the vicinity of the preset repetition frequency range, solving the problem of large initial frequency deviation and inability to directly fine-tune it; the electro-optic modulator component 22 changes the internal refractive index, finely adjusting and correcting the repetition frequency that has entered the coarse-tuning range, eliminating minor deviations, and ensuring that the repetition frequency of the output laser strictly conforms to the preset value, thus achieving precise and efficient closed-loop correction of the repetition frequency of the fiber laser.

[0090] While specific embodiments of this application have been described in detail by way of examples, those skilled in the art should understand that the examples are for illustrative purposes only and not intended to limit the scope of this application. Those skilled in the art should also understand that various modifications can be made to the embodiments without departing from the scope and spirit of this application. The scope of this application is defined by the appended claims.

Claims

1. A fiber laser with tunable repetition frequency, characterized in that, The fiber laser includes a mode-locked laser optical path and a spatial optical path adjustment module; The spatial optical path adjustment module is located inside the mode-locked laser optical path. The spatial optical path adjustment module includes a piezoelectric ceramic component and an electro-optic modulator component. The piezoelectric ceramic component and the electro-optic modulator component lock the repetition frequency of the fiber laser through voltage coordinated adjustment, so that the fiber laser outputs laser that conforms to the preset repetition frequency.

2. The fiber laser according to claim 1, characterized in that, The mode-locked laser optical path is a ring-shaped mode-locked laser optical path, and the fiber laser also includes a reflection filtering module; The annular mode-locked laser optical path forms a closed laser transmission path, and the reflection filter module is disposed at the end of the linear part of the annular mode-locked laser optical path; The spatial optical path adjustment module is disposed inside the loop of the annular mode-locked laser optical path. The spatial optical path adjustment module includes a piezoelectric ceramic component and an electro-optic modulator component. The piezoelectric ceramic component and the electro-optic modulator component lock the repetition frequency of the fiber laser through voltage coordinated adjustment, so that the fiber laser outputs laser that conforms to the preset repetition frequency.

3. The fiber laser according to claim 2, characterized in that, The ring mode-locked laser optical path includes at least a wavelength division multiplexer, a gain fiber, a first fiber coupler, a fiber phase shifter, and a second fiber coupler. The components in the ring mode-locked laser optical path are connected sequentially through optical fibers to form a ring structure.

4. The fiber laser according to claim 3, characterized in that, The ring mode-locked laser optical path also includes a pump laser, wherein the output end of the pump laser is connected to the input end of the wavelength division multiplexer, and is used to provide pump light to the gain fiber.

5. The fiber laser according to claim 3, characterized in that, The input end of the spatial optical path adjustment module is connected to the output end of the first optical fiber coupler, and the output end of the spatial optical path adjustment module is connected to the input end of the optical fiber phase shifter.

6. The fiber laser according to claim 3, characterized in that, The reflection filtering module is a chirped fiber grating, and the reflection filtering module is connected to the output end of the second fiber coupler; The reflection filtering module is used to realize laser reflection, limit the center wavelength and spectral width of the laser, and compensate for the dispersion of other optical fibers in the annular mode-locked laser optical path.

7. The fiber laser according to claim 3, characterized in that, The fiber laser also includes a first output isolator and a photoelectric converter. The input end of the first output isolator is connected to the branch output end of the second fiber coupler, and the output end of the first output isolator is connected to the input end of the photoelectric converter. The first output isolator is used to prevent external reflected light from entering the annular mode-locked laser optical path, and the photoelectric converter is used to convert the laser signal into an electrical signal to detect the repetition frequency.

8. The fiber laser according to claim 7, characterized in that, The fiber laser also includes a servo control system, which is electrically connected to the piezoelectric ceramic component, the electro-optic modulator component, and the photoelectric converter, respectively. The servo control system is used to acquire the laser repetition frequency detected by the photoelectric converter. First, it controls the voltage applied to the piezoelectric ceramic component to make the laser repetition frequency fall into a first preset frequency range. Then, it controls the voltage applied to the electro-optic modulator component to stabilize the laser repetition frequency in a second preset frequency range. The first preset frequency range and the second preset frequency range are centered on the preset repetition frequency, and the second preset frequency range is smaller than the first preset frequency range.

9. The fiber laser according to claim 8, characterized in that, The servo control system includes a microprocessor, a D / A conversion module, and a signal acquisition module; The signal acquisition module is electrically connected to the photoelectric converter and is used to acquire the electrical signal output by the photoelectric converter and convert it into a digital signal for transmission to the microprocessor. The microprocessor is used to output voltage control signals to the piezoelectric ceramic component and the electro-optic modulator component respectively through the D / A conversion module based on the difference between the digital signal and the first preset frequency range and the second preset frequency range.

10. The fiber laser according to claim 2, characterized in that, The spatial optical path adjustment module further includes a first collimator and a second collimator. The first collimator and the piezoelectric ceramic component are fixed together. The first collimator converts the transmission mode of the laser inside the annular mode-locked laser optical path from optical fiber transmission to spatial transmission. The second collimator is fixed together with the electro-optic modulator component through an adapter. The second collimator converts the transmission mode from the spatial transmission mode back to the optical fiber transmission mode.

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