High-energy pulse column vector fiber laser

Abstract

The invention discloses a high-energy pulse column vector fiber laser, which comprises a gain switch pulse seed source, a pre-amplification unit, a mode conversion unit and a main amplification unit which are arranged in sequence, wherein the pre-amplification unit comprises a pre-amplification beam combiner and a pre-amplification double-cladding gain optical fiber which are arranged in sequence, and the pumping end of the pre-amplification beam combiner is connected with a pre-amplification pumping source; the mode conversion unit comprises a mode converter and a polarization controller which are arranged in sequence; the main amplification unit comprises a beam splitter, a plurality of paths of main amplification channels and an optical fiber coupler which are arranged in sequence; wherein each main amplification channel comprises a main amplification beam combiner, a main amplification double-cladding gain optical fiber and a phase delayer which are arranged in sequence, and the pumping end of the main amplification beam combiner is connected with a main amplification pumping source. The pulse column vector fiber laser is combined with a column vector light mode converter and a fiber amplification structure outside a cavity, and high-quality, high-stability and adjustable-repetition-frequency high-power pulse column vector fiber laser output is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser, in particular to a high-energy pulse column vector fiber laser. BACKGROUND

[0002] Column vector laser includes radial polarization light (TM 01 mode) and angular polarization light (TE 01 mode), which has the characteristics of axisymmetric polarization and annular intensity distribution, and a unique and strong local longitudinal electric field is formed under the radial polarization light intensity focusing condition, the polarization direction of the angular polarization light is distributed along the circumference, and a strong longitudinal magnetic field hot spot is generated after high-NA focusing and forms an annular focal spot, so it has unique application advantages in the fields of industrial processing, material processing, particle manipulation, microscopic imaging, etc.

[0003] The column vector light generation method mainly includes two categories: free space scheme and fiber scheme: the free space scheme uses spatial conversion elements (such as birefringent crystal, subwavelength grating mirror, Q wave plate, S wave plate, etc.) to obtain LP 01 mode from LP 11 mode; the fiber scheme uses mode selection coupler, long period fiber grating, femtosecond laser written refractive index modulation structure, etc., which can effectively couple the fundamental mode to the high-order mode with radial or angular polarization characteristics.

[0004] Combining pulsed laser with column vector light can simultaneously utilize the high peak power characteristics in the time domain and the unique mode advantages of the spatial polarization structure, thereby significantly improving the comprehensive performance of the laser system. There are two kinds of technical schemes for generating pulsed column vector light at present: one is to directly generate pulsed column vector mode in the fiber cavity, that is, to integrate mode selection and pulse generation mechanism (such as passive mode locking, active mode locking or Q switching) into the fiber resonant cavity, and to realize pulsed oscillation of vector mode through in-cavity mode control. For example, combining mode conversion devices with mode locking elements to directly generate pulsed vector light can realize high-purity column vector pulse output in the cavity and maintain the compactness and stability of the all-fiber structure. The other is to generate column vector light in free space or external cavity and then convert the conventional pulsed light source, that is, to use mode conversion devices to convert the generated pulsed light into radial or angular polarization column vector light.

[0005] The main way of the existing pulsed column vector fiber laser is to generate picosecond, nanosecond, millisecond pulsed column vector light by mode locking and active modulation and to add mode conversion devices in the cavity. This scheme can generate pulsed column vector light, but still has the following problems: 1. High structural complexity To simultaneously achieve vector mode maintenance, polarization control, and mode-locking conditions within the cavity, multiple optical elements (such as special phase plates, mode selection elements, waveplates, and dispersion compensators) are required, thus complicating the cavity structure. Inserting these elements into the resonant cavity simultaneously affects the mode structure, group delay dispersion, cavity loss, and polarization distribution. The inter-coupling of these parameters results in a very small tolerance window for the cavity design. For example, even a slight change in the position of an element or a deviation in the dispersion compensation amount can cause a switching of the mode's polarization state or a loss of mode-locking.

[0006] 2. Insufficient output stability Nonlinear polarization rotation and passive mode-locking are sensitive to polarization state, intracavity optical power distribution, and external disturbances. Temperature changes or mechanical vibrations can lead to interruptions in mode-locking, pulse instability, and continuous changes in the purity of the output cylindrical vector light mode, requiring frequent readjustment of the polarization controller to maintain a stable mode-locking state. Furthermore, since the polarization and phase distribution of the cylindrical vector light are highly dependent on the precise phase relationship between two degenerate higher-order modes, frequent readjustment of the polarization controller can disrupt the phase balance. When this balance is broken, the cylindrical vector polarization state easily collapses, degenerating into a linearly polarized fundamental mode or an unstable hybrid mode, failing to output the desired radially and angularly polarized light. Therefore, through intracavity LP... 11 The resonance-generated pulse column vector light, due to the cross-correlation of multiple devices, increases the stability of its operation and brings with it the difficulty of engineering.

[0007] 3. Adjustable range is limited. The repetition frequency of active mode-locked pulses is limited by the cavity length or the modulator synchronization frequency, while the pulse characteristics of passive mode-locked pulses are determined by the coupling of nonlinear effects and cavity structure, limiting the tunability of the repetition frequency. Furthermore, both methods typically require adjusting the cavity length or resetting the operating point when changing the repetition frequency, resulting in complex operations and a limited adjustable range. Under high-power conditions, the accumulation of nonlinearity within the cavity may further limit the expansion of the repetition frequency and the flexible adjustment of pulse parameters.

[0008] 4. Output power is limited. Because generating cylindrical vector light within the cavity relies on specific mode-changing devices, these devices must be placed directly within the laser cavity and withstand high round-trip power. Once mode-locking is established within the cavity, the peak power increases significantly, making these components susceptible to thermal effects, thin-film ablation, or surface damage. This reduces the device's lifespan, limits the laser's maximum output power, and prevents linear control of the output power. Furthermore, existing solutions produce relatively low vector light power, typically in the mW to W range, which severely restricts the application of cylindrical vector fiber lasers. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention provides a high-power, high-energy pulsed column vector fiber laser with a compact structure, high environmental stability, wide-range tunable repetition frequency, and the ability to achieve high peak power output.

[0010] This invention discloses a high-energy pulsed column vector fiber laser, characterized in that it comprises: a gain-switching pulse seed source, a pre-amplification unit, a mode conversion unit, and a main amplification unit arranged sequentially; The pre-amplification unit includes a pre-amplification pump source, a pre-amplification combiner, and a pre-amplification double-clad gain fiber. The output end of the gain-switching pulse seed source is connected to the signal end of the pre-amplification combiner, the output end of the pre-amplification pump source is connected to the pump end of the pre-amplification combiner, and the output end of the pre-amplification combiner is connected to the input end of the pre-amplification double-clad gain fiber. The mode conversion unit includes a mode converter and a polarization controller. The output end of the pre-amplified double-clad gain fiber is connected to the input end of the mode converter, and the output end of the mode converter is connected to the input end of the polarization controller. The main amplification unit includes a beam splitter, multiple main amplification channels, and an optical fiber coupler. The output of the polarization controller is connected to the output of the beam splitter. Multiple outputs of the beam splitter are correspondingly connected to multiple main amplification channels. The outputs of the main amplification channels are connected to the inputs of the optical fiber couplers. The output of the optical fiber couplers outputs a high-power pulsed beam. Each main amplification channel includes a main amplification pump source, a main amplification combiner, a main amplification double-clad gain fiber, and a phase delayer. The output of the main amplification pump source is connected to the pump end of the main amplification combiner. The signal end of the main amplification combiner is connected to one output of the beam splitter. The output of the main amplification combiner is connected to the input of the main amplification double-clad gain fiber. The output of the main amplification double-clad gain fiber is connected to the input of the phase delayer. The output of the phase delayer is connected to one input of the optical fiber coupler.

[0011] As a further improvement of the present invention, the pre-amplification unit further includes: an isolator; Along the optical path transmission direction, the isolator is disposed between the gain switch pulse seed source and the pre-amplification combiner; that is, the output terminal of the gain switch pulse seed source is connected to the input terminal of the isolator, and the output terminal of the isolator is connected to the signal terminal of the pre-amplification combiner.

[0012] As a further improvement of the present invention, the pre-amplification unit further includes: a first cladding light stripper; Along the optical path transmission direction, the first cladding optical stripper is disposed between the pre-amplified double-clad gain fiber and the mode converter, that is, the output end of the pre-amplified double-clad gain fiber is connected to the input end of the first cladding optical stripper, and the output end of the first cladding optical stripper is connected to the input end of the mode converter.

[0013] As a further improvement of the present invention, the main amplification unit further includes: a vector light isolator; Along the optical path transmission direction, the vector optical isolator is disposed between the polarization controller and the beam splitter, that is, the output end of the polarization controller is connected to the input end of the vector optical isolator, and the output end of the vector optical isolator is connected to the input end of the beam splitter.

[0014] As a further improvement of the present invention, the main amplification unit further includes: a second cladding light stripper; The output end of the fiber coupler is connected to the input end of the second cladding light stripper, and the output end of the second cladding light stripper outputs a high-power pulse beam.

[0015] As a further improvement of the present invention, the gain-switching semiconductor pulse seed source includes one of a semiconductor laser and a narrow linewidth laser.

[0016] As a further improvement of the present invention, the mode converter includes a mode selection coupler and a long-period fiber grating, as well as a mode conversion module based on S-wave plates, Q-wave plates, LCPs, etc., which are fiberized through micro-optical elements.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Reduce system structural complexity To address the issue that existing optical structures are overly complex due to multiple optical elements within the cavity, this invention proposes a technical solution for achieving cylindrical vector light output outside the cavity. This solution separates the pulse generation scheme from the generation of cylindrical vector light, reducing the complexity of the overall optical path structure, decreasing the cross-correlation of optical devices, and thus improving the reliability of the optical structure.

[0018] 2. Improve the stability of pulse column vector light output. To address the instability of output pulses and mode field distortion caused by changes in the operating state of existing intracavity mode conversion devices, this invention constructs a scheme for generating pulse column vector light that is insensitive to polarization and can maintain stable output over a long period of time.

[0019] 3. Expand the adjustable range of repetition frequency and simplify the adjustment method. Traditional mode-locked modulation and active modulation of repetition frequency are limited by cavity length or require resetting the operating point, making the adjustment process complex and the variable range limited. This invention provides an electronic control method that directly modulates the pump current of the gain medium at high speed to achieve pulse generation and repetition frequency control, thereby making pulse parameter adjustment more flexible. Combined with an external mode conversion device, a pulse column vector light parameter scheme that can be adjusted more flexibly is obtained.

[0020] 4. More flexible power adjustment In view of the fact that existing devices are easily damaged due to the conversion within the cavity, the present invention provides a solution in which the power can be linearly adjusted, making the system more suitable for stable output of high-power, high-energy pulse column vector light.

[0021] In summary, this invention completely decouples pulse generation from vector mode generation, eliminating the need for the laser cavity to simultaneously maintain high-order modes and complex polarization structures. This significantly reduces the complexity of the intracavity structure and its sensitivity to environmental disturbances, thereby improving system stability. Simultaneously, the external converter can withstand higher power and independently optimize mode purity and polarization state, making the system easier to achieve high-power, high-energy output and exhibiting better modularity, adaptability, and engineering feasibility. This invention proposes a technical solution for generating stable pulsed light using a gain-switched laser, and further combines it with an external cylindrical vector light mode converter and fiber amplification structure to obtain high-quality, high-stability, and tunable high-power pulsed cylindrical vector fiber laser output. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the high-energy pulsed column vector fiber laser disclosed in this invention; Figure 2 The diagrams show signal pulses using and without a phase delayer, as disclosed in this invention.

[0023] In the picture: 1. Gain-switched pulse seed source; 2. Isolator; 3. Pre-amplified pump source; 4. Pre-amplified combiner; 5. Pre-amplified double-clad gain fiber; 6. First cladding optical stripper; 7. Mode converter; 8. Polarization controller; 9. Vector optical isolator; 10. Beam splitter; 11. First pump source; 12. Second pump source; 13. Third pump source; 14. First main amplification combiner; 15. Second main amplification combiner; 16. Third main amplification combiner; 17. First main amplification double-clad gain fiber; 18. Second main amplification double-clad gain fiber; 19. Third main amplification double-clad gain fiber; 20. First phase delayer; 21. Second phase delayer; 22. Third phase delayer; 23. Fiber coupler; 24. Second cladding optical stripper. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] The present invention will now be described in further detail with reference to the accompanying drawings: This invention provides a high-energy pulsed column vector fiber laser, which directly generates pulsed signal light through gain switching. Preferably, laser mode conversion is performed through an external cavity structure, and the obtained column vector light is used as signal light in the subsequent fiber amplification structure using double-clad gain fiber amplification. Through beam combining, it ultimately achieves "high repetition rate + high peak power + high mode stability" that traditional mode-locking and Q-switching techniques cannot achieve simultaneously. This column vector fiber laser features a compact structure, high environmental stability, wide-range tunable repetition rate, high peak power output, and high-energy pulses.

[0026] like Figure 1 As shown, the high-energy pulsed column vector fiber laser of the present invention includes a gain-switched pulse seed source 1, a pre-amplification unit, a mode conversion unit, and a multi-channel main amplification unit connected in sequence; wherein, The gain-switching semiconductor pulse seed source 1 of the present invention is used to generate pulse signal light with a stable repetition frequency and controllable time width; wherein, the gain-switching semiconductor pulse seed source 1 can be a semiconductor laser, a narrow linewidth laser, or other types, and the wavelength range can be 532±10nm, 1064±10nm, 1.5μm, 2μm, etc., covering multiple bands of visible light, near infrared and far infrared.

[0027] The pre-amplification unit of this invention includes an isolator 2, a pre-amplification pump source 3, a pre-amplification combiner 4, a pre-amplification double-clad gain fiber 5, and a first clad optical stripper 6. The output of the gain-switching pulse seed source 1 is connected to the input of the isolator 2. The output of the isolator 2 is connected to the signal terminal of the pre-amplification combiner 4. The output of the pre-amplification pump source 3 is connected to the pump terminal of the pre-amplification combiner 4. The output of the pre-amplification combiner 4 is connected to the input of the pre-amplification double-clad gain fiber 5. The output end of the fiber 5 is connected to the input end of the first cladding light stripper 6; wherein, the isolator 2 is used to block the backlight from entering the seed source, thereby improving the stability of the overall system; the pre-amplified pump source 3 is a semiconductor laser with a center wavelength of 976nm, and its output is input through the pump end of the pre-amplified beam combiner 4; the seed pulse light enters the signal end of the beam combiner 4 after passing through the isolator 2, and is injected into the double-clad fiber 5 together with the pump light after multiplexing, so as to realize the pre-amplification of the signal pulse; the pre-amplified output is removed by the cladding light stripper 6 to remove residual pump light.

[0028] The mode conversion unit of the present invention includes a mode converter 7 and a polarization controller 8. The output end of the first cladding stripper 6 is connected to the input end of the mode converter 7, and the output end of the mode converter 7 is connected to the input end of the polarization controller 8. The laser after removing residual pump light is converted into cylindrical vector light by the mode converter 7, and then the polarization state is adjusted by the polarization controller 8 to output radially polarized light or angularly polarized light.

[0029] The multi-channel main amplification unit of the present invention includes a vector optical isolator 9, a beam splitter 10, multiple main amplification channels, an optical fiber coupler 23, and a second cladding light stripper 24. The output terminal of the polarization controller 8 is connected to the input terminal of the vector optical isolator 9, and the output terminal of the vector optical isolator 9 is connected to the input terminal of the beam splitter 10. Multiple output terminals of the beam splitter 10 are correspondingly connected to the multiple main amplification channels. The output terminals of the main amplification channels are connected to the input terminals of the optical fiber coupler 23, and the output terminals of the optical fiber coupler 23 are connected to the input terminals of the second cladding light stripper 24. The output terminals of the second cladding light stripper 24 are connected to the input terminals of the second cladding light stripper 24. The output end produces a high-power pulsed beam. Each main amplification channel includes a main amplification pump source, a main amplification combiner, a main amplification double-clad gain fiber, and a phase delayer. The output end of the main amplification pump source is connected to the pump end of the main amplification combiner. The signal end of the main amplification combiner is connected to one output end of the beam splitter. The output end of the main amplification combiner is connected to the input end of the main amplification double-clad gain fiber. The output end of the main amplification double-clad gain fiber is connected to the input end of the phase delayer. The output end of the phase delayer is connected to one input end of the fiber coupler. Preferably, this invention employs three main amplification channels. The three amplified and phase-modulated pulsed beams are combined outside the cavity in a 1×3 fiber coupler 23 and output as a high-power pulsed beam via a second cladding stripper 24. Specifically, the radially polarized or angularly polarized light output by the polarization controller 8 is isolated by a vector light isolator 9 and then fed into the beam splitter 10. The three signal beams output by the beam splitter 10 enter the three main amplification channels respectively; that is, the first signal beam enters the signal end of the first main amplification combiner 14, and after being multiplexed with the pump light of the first main amplification pump source 11 in the first main amplification combiner 14, it is injected into the first main amplification double-clad gain fiber 17 to achieve main amplification; the second signal beam enters the signal end of the second main amplification combiner 15, and after being multiplexed with the pump light of the second main amplification pump source 12 in the second main amplification combiner 15, it is injected into the second main amplification double-clad gain fiber 18 to achieve main amplification; the third signal beam enters the signal end of the third main amplification combiner 16, and after being multiplexed with the pump light of the third main amplification pump source 13 in the third main amplification combiner 16, it is injected into the third main amplification double-clad gain fiber 19 to achieve main amplification. Each main amplifier output is connected in series with a phase delay unit. Specifically, the output of the first main amplifier double-clad gain fiber 17 is connected in series with a first phase delay unit 20, the output of the second main amplifier double-clad gain fiber 18 is connected in series with a second phase delay unit 21, and the output of the third main amplifier double-clad gain fiber 19 is connected in series with a third phase delay unit 21. By precisely adjusting the fiber length, the phase of the three output pulses is synchronously controlled to meet the time-domain matching requirements of different pulse widths.

[0030] The three phase-modulated signal beams are superimposed in an external optical cavity within a 1×3 fiber coupler 23. Without the first phase delayer 20 to the third phase delayer 22, the amplified pulsed light signals would suffer from time-domain mismatch, leading to pulse signal asynchrony and preventing maximum pulse energy superposition during beam combining. Figure 2 As shown. Therefore, by using a phase delayer, a pulse vector beam with higher peak power and energy can be superimposed. The second cladding light stripper 24 is located at the output end of the 1×3 fiber coupler 23 to remove residual pump components and improve the output beam quality. The final output fiber end can adopt an 8° angle end face structure to suppress further return light from entering the system, thereby improving the long-term stability of the system operation.

[0031] The advantages of this invention are: This invention utilizes a gain-switched pulse seed source and a mode-converting device to perform mode conversion of the gain-switched pulse light outside the cavity, resulting in a stable, higher mode purity, and more flexible power adjustment pulse-column vector light. Simultaneously, high-damage-threshold components can be freely selected outside the cavity, ensuring that the pulse-column vector mode possesses good polarization and higher power before entering the amplification link. This lays the foundation for mode preservation and low-loss amplification in subsequent double-clad gain fibers, thereby significantly improving the final mode stability and beam quality of the laser.

[0032] This invention utilizes a gain-switched laser combined with a mode-switching device in its optical path structure. By controlling the signal amplitude, bias current, and modulation depth, it can achieve rapid switching output at the millisecond, ps, and ns levels. By merging radial, angular, and mixed modes, it can obtain a high-repetition-rate, high-energy column vector laser, covering wavelength ranges of 532±10nm, 1064±10nm, 1.5μm, and 2μm, encompassing multiple bands of visible light, near-infrared, and far-infrared.

[0033] This invention employs a multi-beam splitting amplification unit and achieves precise timing matching of multi-channel pulse signals by setting adjustable phase delayers separately. By splitting a single vector pulse light into N pulse lights and amplifying them separately using MOPA, the pulse light can be amplified N times after beam combining, resulting in a higher energy and higher power pulse column vector light output.

[0034] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high energy pulsed column vector fiber laser characterized by, The application relates to a high-power pulsed laser amplifier. The gain-switched pulsed seed source, the pre-amplification unit, the mode conversion unit and the main amplification unit are sequentially arranged. The pre-amplification unit comprises a pre-amplification pump source, a pre-amplification combiner and a pre-amplification double-clad gain fiber, the output end of the gain-switched semiconductor pulsed seed source is connected with the signal end of the pre-amplification combiner, the output end of the pre-amplification pump source is connected with the pump end of the pre-amplification combiner, and the output end of the pre-amplification combiner is connected with the input end of the pre-amplification double-clad gain fiber. The mode conversion unit comprises a mode converter and a polarization controller, the output end of the pre-amplification double-clad gain fiber is connected with the input end of the mode converter, and the output end of the mode converter is connected with the input end of the polarization controller. The main amplification unit comprises a beam splitter, a plurality of main amplification channels and a fiber coupler, the output end of the polarization controller is connected with the output end of the beam splitter, a plurality of output ends of the beam splitter are correspondingly connected with the plurality of main amplification channels, the output ends of the main amplification channels are connected with the input ends of the fiber coupler, and the output end of the fiber coupler outputs a high-power pulsed laser beam; wherein each main amplification channel comprises a main amplification pump source, a main amplification combiner, a main amplification double-clad gain fiber and a phase delay device, the output end of the main amplification pump source is connected with the pump end of the main amplification combiner, the signal end of the main amplification combiner is connected with one output end of the beam splitter, the output end of the main amplification combiner is connected with the input end of the main amplification double-clad gain fiber, the output end of the main amplification double-clad gain fiber is connected with the input end of the phase delay device, and the output end of the phase delay device is connected with one input end of the fiber coupler.

2. The high energy pulsed column vector fiber laser of claim 1, wherein, The pre-amplification unit further comprises an isolator. The isolator is arranged between the gain-switched pulsed seed source and the pre-amplification combiner in the light path transmission direction.

3. The high energy pulsed column vector fiber laser of claim 1, wherein, The pre-amplification unit further comprises a first cladding light stripper. The first cladding light stripper is arranged between the pre-amplification double-clad gain fiber and the mode converter in the light path transmission direction.

4. The high energy pulsed column vector fiber laser of claim 1, wherein, The main amplification unit further comprises a vector light isolator. The vector light isolator is arranged between the polarization controller and the beam splitter in the light path transmission direction.

5. The high energy pulsed column vector fiber laser of claim 1, wherein, The main amplification unit further comprises a second cladding light stripper. The output end of the fiber coupler is connected with the input end of the second cladding light stripper, and the output end of the second cladding light stripper outputs a high-power pulsed laser beam.

6. The high energy pulsed column vector fiber laser of any of claims 1-5, wherein, The gain-switched semiconductor pulsed seed source comprises one of a semiconductor laser and a narrow-line-width laser.

7. The high energy pulsed column vector fiber laser of any of claims 1-5, wherein, The mode converter comprises one of a mode selection coupler, a long-period fiber grating and a mode conversion module based on an S-wave plate, a Q-wave plate, an LCP and the like through micro-optical element fiberization.

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