All-fiber ultrafast laser based on 1.7-micron high energy

Abstract

The invention provides an all-fiber ultrafast laser based on 1.7 micron high energy. The all-fiber ultrafast laser comprises a pumping source, a wavelength division multiplexer, a gain fiber, a band-pass filter, an output coupler, a single-mode fiber, a first three-ring polarization controller, a polarization dependent isolator and a second three-ring polarization controller. The output end of the pumping source is connected with the wavelength division multiplexer, the output end of the wavelength division multiplexer is connected with the band-pass filter through the gain fiber, the output end of the band-pass filter is connected with the output coupler, and the first output port of the output coupler is connected with the input end of the first three-ring polarization controller through the single-mode fiber. A second output port of the output coupler is used as the output of the all-fiber ultrafast laser, the output end of the first three-ring polarization controller is connected with the polarization dependent isolator, the output end of the polarization dependent isolator is connected with the second three-ring polarization controller, and the output end of the second three-ring polarization controller is connected with the wavelength division multiplexer.

Description

Technical Field

[0001] The invention relates to the fields of laser technology and nonlinear optical technology, and in particular to an all-fiber ultrafast laser based on 1.7 micron high energy. Background Art

[0002] The 1.7μm band laser has unique spectral characteristics and has great application value in many fields, and has attracted more and more attention from researchers. The 1.7μm band is located at the absorption peak of carbon-hydrogen bonds. Lasers in this band can be used for targeted skin treatment of lipids / fat, processing and welding of plastics or certain polymers, and detection of organic gases such as methane. In addition, water molecules have a low absorption rate in the 1.7μm band, and pulsed laser light sources in this band are important tools for biological imaging. The absorption peak of dysprosium ions is also located in the 1.7μm band, so 1.7μm band lasers can also be used to pump dysprosium-doped soft glass fibers to produce mid-infrared lasers. Compared with other types of 1.7μm band lasers such as solid-state lasers, 1.7μm band fiber lasers have the advantages of high efficiency, good beam quality, compact structure and easy integration, convenient thermal management, and flexible operation, and have received widespread attention.

[0003] Compared with the near-infrared (mainly 1.0μm and 1.5μm) band, the operating wavelength of the 1.7μm band fiber laser is longer, that is, its self-focusing threshold and the threshold of nonlinear effect will be higher, which means that the 1.7μm band fiber laser will have more potential in suppressing nonlinear effects than the 1.0μm and 1.5μm fiber lasers. At present, the output of 1.7μm band lasers is usually achieved by using Tm3+ doped or Tm3+ and Ho3+ co-doped fiber as the gain medium. Compared with Tm3+ and Ho3+ co-doped fiber, Tm3+ doped fiber lasers have more advantages in laser conversion efficiency and performance.

[0004] In recent years, with the advancement of fiber manufacturing technology and in-depth research on new mode-locking mechanisms, passive mode-locked fiber lasers have developed rapidly, the performance of mode-locked fiber lasers has gradually improved, and the single pulse energy has also been further improved. However, compared with the mode-locked fiber lasers in the 1-1.5μm band, the 1.7μm band gain fiber has a large anomalous dispersion, so the peak power in the cavity is clamped to a small value, and the peak power cannot be increased with the increase of pump power. In addition, this type of mode-locked fiber laser usually operates in soliton mode, and the pulse energy is limited by the soliton area theorem, which is much lower than the mode-locked fiber laser in the 1-1.5μm band. At present, the single pulse energy obtained by the fiber laser that realizes the output of the 1.7μm band laser is mostly below nanojoules, and there are some problems such as gain-related modulation instability caused by the large anomalous dispersion characteristics of the gain fiber in this type of fiber laser. Therefore, it is necessary to explore high-energy 1.7μm band mode-locked fiber lasers, which is of great significance for the development of compact, efficient and reliable ultrashort pulse laser systems. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention aims to provide an all-fiber ultrafast laser based on 1.7 μm high energy. The present invention can make the laser more stable and reliable, and break through the limitation of low output pulse energy of 1.7 μm band all-fiber laser.

[0006] The first aspect of the present application provides an all-fiber ultrafast laser based on 1.7 micron high energy. The all-fiber ultrafast laser based on 1.7 micron high energy includes: a pump source 1, a wavelength division multiplexer 2, a gain fiber 3, a bandpass filter 4, an output coupler 5, a single-mode fiber 6, a first three-ring polarization controller 7, a polarization-dependent isolator 8, and a second three-ring polarization controller 9;

[0007] Wherein, the optical fiber output end of the pump source 1 is connected to the input end of the wavelength division multiplexer 2, the output end of the wavelength division multiplexer 2 is connected to the input end of the bandpass filter 4 through the gain optical fiber 3, the output end of the bandpass filter 4 is connected to the input end of the output coupler 5, the first output port of the output coupler 5 is connected to the input end of the first three-ring polarization controller 7 through the single-mode optical fiber 6, the second output port of the output coupler 5 serves as the output of the all-fiber ultrafast laser, the output end of the first three-ring polarization controller 7 is connected to the input end of the polarization-dependent isolator 8, the output end of the polarization-dependent isolator 8 is connected to the input end of the second three-ring polarization controller 9, and the output end of the second three-ring polarization controller 9 is connected to the input end of the wavelength division multiplexer 2;

[0008] The wavelength division multiplexer 2, the gain optical fiber 3, the bandpass filter 4, the output coupler 5, the single-mode optical fiber 6, the first three-ring polarization controller 7, the polarization-dependent isolator 8, and the second three-ring polarization controller 9 constitute a ring cavity;

[0009] The first three-ring polarization controller 7, the polarization-dependent isolator 8 and the second three-ring polarization controller (9) constitute a nonlinear polarization rotation structure, which can be used as an equivalent saturable absorber to achieve mode locking. The saturable absorption effect generated by the nonlinear polarization rotation structure can achieve self-amplitude modulation.

[0010] The nonlinear polarization rotation (NPR) structure can be used as an equivalent saturable absorber to achieve mode locking. At the same time, the saturable absorption effect produced by the nonlinear polarization rotation structure can achieve self-amplitude modulation. The mutual balance between the structure and physical processes such as group velocity dispersion and nonlinear effects is an important factor in suppressing modulation instability and achieving stable pulses.

[0011] In combination with the first aspect, in a possible implementation, the output coupler 5 is connected to the single-mode optical fiber 6 by fiber fusion splicing, and when performing fiber fusion splicing, the loss is controlled within 0.05 dB.

[0012] In combination with the first aspect, in a possible implementation, the pump source 1 is a fiber laser with a central wavelength of 1570 nanometers, and the output end of the pump source 1 is a fiber output with a maximum power of 2 watts.

[0013] In combination with the first aspect, in a possible implementation, the wavelength division multiplexer 2 is a 1570 nanometer or 1750 nanometer optical fiber wavelength division multiplexer 2, and the pump light emitted by the pump source 1 is coupled through the wavelength division multiplexer 2 and injected into the gain optical fiber 3.

[0014] In combination with the first aspect, in a possible implementation manner, the gain fiber 3 is a thulium-doped fiber.

[0015] In combination with the first aspect, in a possible implementation, the bandpass filter 4 is an all-fiber bandpass filter, and the overall structure is composed of an input optical fiber, a collimator, a filter, a focusing lens, and an output optical fiber. Compared with the commonly used spatial structure optical filter, it has the characteristics of simple structure, small size, low production cost, low insertion loss, and insensitivity to polarization, which can effectively reduce the complexity of the system while ensuring the integrity of the optical signal.

[0016] In combination with the first aspect, in a possible implementation manner, the bandpass filter 4 is an all-fiber bandpass filter with a passband wavelength range of 1700±49 nm and an insertion loss of 1.3 dB.

[0017] In combination with the first aspect, in a possible implementation manner, the polarization-dependent isolator 8 is a fiber polarization-dependent isolator, whose isolation is 34 dB and insertion loss is 0.88 dB.

[0018] In combination with the first aspect, in a possible implementation, the single-mode optical fiber 6 is an SMF-28e single-mode optical fiber.

[0019] In combination with the first aspect, in a possible implementation manner, a coupling ratio between the first output port and the second output port of the output fiber coupler is 80:20.

[0020] The 1.7-micron high-energy all-fiber ultrafast laser provided by the present invention uses an all-fiber bandpass filter combined with a nonlinear polarization rotation mode-locked structure, which overcomes the problem that the energy of the traditional mode-locked pulse generated is usually below 0.1 nanojoules, and achieves high-energy pulse output in this band. Among them, the gain fiber is a thulium-doped fiber, and the gain spectrum it produces is 1700-2100nm. An all-fiber bandpass filter is added to the ring cavity, and the passband wavelength range is 1700-1800nm, which can make the wavelength of the output laser in the 1.7-micron band (1700-1800nm). In addition, the present invention is composed of all-fiber devices, with a simple structure, stable and reliable, easy to operate, and has important academic research significance and industrial application potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A schematic diagram of the structure of a 1.7 micron high-energy all-fiber ultrafast laser provided in an embodiment of the present application;

[0022] Figure 2 It is a structural schematic diagram of a bandpass filter provided by the present invention;

[0023] Figure 3 This is a mode-locked pulse spectrum diagram of a 1.7-micron high-energy all-fiber ultrafast laser at 800 mW provided by the present invention;

[0024] Figure 4 This is a timing diagram of a mode-locked pulse of a 1.7-micron high-energy all-fiber ultrafast laser at 800 mW provided by the present invention;

[0025] Figure 5 This is a mode-locked pulse radio frequency diagram of a 1.7-micron high-energy all-fiber ultrafast laser at 800 mW provided by the present invention;

[0026] Figure 6 This is a graph of the autocorrelation of a mode-locked pulse of a 1.7-micron high-energy all-fiber ultrafast laser at 800 mW provided by the present invention;

[0027] Figure 7 This is a relationship diagram between the output energy and average output power of a mode-locked pulse based on a 1.7-micron high-energy all-fiber ultrafast laser provided by the present invention at different pump powers;

[0028] Figure 8 This is a spectrum diagram of a 1.7 micron high-energy all-fiber ultrafast laser provided by the present invention when outputting continuous light at 2000 mW;

[0029] Fig. 9 The present invention provides a graph showing the average output power variation of continuous light at different pump powers based on a 1.7-micron high-energy all-fiber ultrafast laser. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of this application.

[0031] The term "and / or" in this application can be a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this application generally indicates that the associated objects before and after are in an "or" relationship.

[0032] The terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or modules is not necessarily limited to those steps or modules that are clearly listed, but may include other steps or modules that are not clearly listed or inherent to these processes, methods, products or devices.

[0033] In recent years, with the advancement of fiber manufacturing technology and in-depth research on new mode-locking mechanisms, passive mode-locked fiber lasers have developed rapidly, the performance of mode-locked fiber lasers has gradually improved, and the single pulse energy has also been further improved. However, compared with the mode-locked fiber lasers in the 1-1.5μm band, the 1.7μm band gain fiber has a large anomalous dispersion, so the peak power in the cavity is clamped to a small value, and the peak power cannot be increased with the increase of pump power. In addition, this type of mode-locked fiber laser usually operates in soliton mode, and the pulse energy is limited by the soliton area theorem, which is much lower than the mode-locked fiber laser in the 1-1.5μm band. At present, the single pulse energy obtained by the fiber laser that realizes the output of the 1.7μm band laser is mostly below nanojoules, and there are some problems such as gain-related modulation instability caused by the large anomalous dispersion characteristics of the gain fiber in this type of fiber laser. Therefore, it is necessary to explore high-energy 1.7μm band mode-locked fiber lasers, which is of great significance for the development of compact, efficient and reliable ultrashort pulse laser systems.

[0034] Therefore, this application provides an all-fiber ultrafast laser based on 1.7 micron high energy, see Figure 1 The 1.7 micron high energy all-fiber ultrafast laser comprises: a pump source 1, a wavelength division multiplexer 2, a gain fiber 3, a bandpass filter 4, an output coupler 5, a single-mode fiber 6, a first three-ring polarization controller 7, a polarization-dependent isolator 8, and a second three-ring polarization controller 9;

[0035] Wherein, the optical fiber output end of the pump source 1 is connected to the input end of the wavelength division multiplexer 2, the output end of the wavelength division multiplexer 2 is connected to the input end of the bandpass filter 4 through the gain optical fiber 3, the output end of the bandpass filter 4 is connected to the input end of the output coupler 5, the first output port of the output coupler 5 is connected to the input end of the first three-ring polarization controller 7 through the single-mode optical fiber 6, the second output port of the output coupler 5 serves as the output of the all-fiber ultrafast laser, the output end of the first three-ring polarization controller 7 is connected to the input end of the polarization-dependent isolator 8, the output end of the polarization-dependent isolator 8 is connected to the input end of the second three-ring polarization controller 9, and the output end of the second three-ring polarization controller 9 is connected to the input end of the wavelength division multiplexer 2;

[0036] The wavelength division multiplexer 2, the gain optical fiber 3, the bandpass filter 4, the output coupler 5, the single-mode optical fiber 6, the first three-ring polarization controller 7, the polarization-dependent isolator 8, and the second three-ring polarization controller 9 constitute a ring cavity;

[0037] The first three-ring polarization controller 7, the polarization-dependent isolator 8 and the second three-ring polarization controller (9) constitute a nonlinear polarization rotation structure, which can be used as an equivalent saturable absorber to achieve mode locking. The saturable absorption effect generated by the nonlinear polarization rotation structure can achieve self-amplitude modulation.

[0038] The nonlinear polarization rotation structure can be used as an equivalent saturable absorber to achieve mode locking. At the same time, the saturable absorption effect produced by the nonlinear polarization rotation structure can achieve self-amplitude modulation. The mutual balance between the structure and physical processes such as group velocity dispersion and nonlinear effects is an important factor in suppressing modulation instability and achieving stable pulses.

[0039] Furthermore, the output coupler 5 is connected to the single-mode optical fiber 6 by optical fiber fusion splicing, and during the optical fiber fusion splicing, the loss is controlled within 0.05 dB.

[0040] Furthermore, the pump source 1 is a fiber laser with a central wavelength of 1570 nanometers, and the output end of the pump source 1 is a fiber output with a maximum power of 2 watts.

[0041] Furthermore, the wavelength division multiplexer 2 is a 1570 nanometer or 1750 nanometer optical fiber wavelength division multiplexer 2 , and the pump light emitted by the pump source 1 is coupled through the wavelength division multiplexer 2 and injected into the gain optical fiber 3 .

[0042] Furthermore, the gain fiber 3 is a thulium-doped fiber.

[0043] Furthermore, the bandpass filter 4 is an all-fiber bandpass filter, see Figure 2 The overall structure consists of an input optical fiber 10, a collimator 11, a filter 12, a focusing lens 13 and an output optical fiber 14. Compared with the commonly used spatial structure optical filter, it has the characteristics of simple structure, small size, low production cost, small insertion loss and insensitivity to polarization, which can effectively reduce the complexity of the system while ensuring the integrity of the optical signal.

[0044] Furthermore, the bandpass filter 4 is an all-fiber bandpass filter with a passband wavelength range of 1700±49nm and an insertion loss of 1.3dB.

[0045] Furthermore, the polarization-dependent isolator 8 is a fiber polarization-dependent isolator, and its isolation is 34 dB and its insertion loss is 0.88 dB.

[0046] Furthermore, the single-mode optical fiber 6 is a SMF-28e single-mode optical fiber.

[0047] Furthermore, the coupling ratio between the first output port and the second output port of the output optical fiber coupler is 80:20.

[0048] The 1.7-micron high-energy all-fiber ultrafast laser provided by the present invention uses an all-fiber bandpass filter combined with a nonlinear polarization rotation mode-locking structure, which overcomes the problem that the energy of the conventional mode-locked pulse generated is usually below 0.1 nanojoules, and achieves high-energy pulse output in this band. In addition, the present invention is composed of all-fiber devices, has a simple structure, is stable and reliable, and is easy to operate, and has important academic research significance and industrial application potential.

[0049] In specific implementation, the pump source 1 is a fiber laser with a central wavelength of 1570nm, which is the pump source of the mode-locked thulium-doped fiber laser described in the present invention. The pump source 1 couples the 1570nm laser into the gain fiber 3 through the 1570 / 1750nm fiber wavelength division multiplexer 2. The gain fiber used here is a thulium-doped fiber with a length of 1m. Then it passes through the bandpass filter 4, which allows the laser within its passband to pass through, while suppressing the laser in other bands from passing through. The laser after passing through the bandpass filter 4 passes through the output coupler 5, and its output coupling ratio is 20:80, which divides the laser into two parts, one end of which 20% is used as the output of the all-fiber laser, and the other end of 80% continues to be transmitted in the cavity, passes through a single-mode optical fiber 6 with a length of about 20m, which is used to accumulate nonlinear effects, and then passes through the first three-ring polarization controller 7, the polarization-dependent isolator 8, the second three-ring polarization controller 9 and other optical devices. The above three optical devices constitute a nonlinear polarization rotation (NPR) structure, wherein the polarization-dependent isolator 8 ensures the unidirectional transmission characteristics of light in the laser cavity and provides polarization selectivity, the first three-ring polarization controller 7 and the second three-ring polarization controller 9 are used to adjust the polarization state of the light transmitted in the cavity, and finally the laser returns to a coupled input port of the wavelength division multiplexer 2, thereby, the above various all-fiber devices constitute a ring optical circuit structure, that is, the all-fiber laser of the ring cavity.

[0050] like Figure 2 As shown, the all-fiber bandpass filter 4 provided by the present invention is composed of an input optical fiber 10, a collimating lens 11, a filter 12, a focusing lens 13, and an output optical fiber in sequence.

[0051] In specific implementation, the laser transmitted by the input optical fiber 10 is converted into a parallel beam through the collimating lens 11, and filtered through the filter 12. The principle is that light of different wavelengths will be reflected and refracted in the filter. By controlling the thickness and refractive index of the filter, the light of a specific wavelength can be enhanced and the light of other wavelengths can be offset during the light interference process, thereby achieving the filtering effect of a specific wavelength band. After filtering, the parallel beam is focused into the core of the output optical fiber 14 by the focusing lens 13. The input optical fiber 11 and the output optical fiber 14 used in the present invention are both SMF-28e single-mode optical fibers.

[0052] When the pump power reaches 800mW, the first three-ring polarization controller 7 and the second three-ring polarization controller 9 are manually adjusted to change the polarization state in the cavity, and a stable mode-locked pulse can be obtained. Figure 3-Figure 6 The output characteristics of the stable mode-locked pulse at a pump power of 800mW are shown, including the spectrum, pulse timing, RF, and autocorrelation curves. Figure 7 The results show the variation of average output power and output energy with pump power. When the pump power increases from 800mW to 2000mW, the pulse state remains unchanged, and the average output power increases from 12.75mW to 63.5mW, and the corresponding pulse energy increases from 2.34nJ to 11.64nJ. The above research results are consistent with the typical characteristics of high-energy pulsed mode-locked fiber lasers. At the same time, the fiber laser also has high-power output characteristics when outputting continuous light. Figure 8 The spectral characteristics of the fiber laser outputting stable continuous light when the pump power is 2000mW are demonstrated. Fig. 9 The paper shows the variation of the average output power of the continuous light of the all-fiber laser in the non-mode-locked state with the change of pump power. When the pump power gradually increases from 800mW to 2000mW, its output power increases from 16.3mW to 68.6mW. In short, the high-energy pulse output in the 1.7μm band is achieved by the mode-locked thulium-doped fiber laser based on the nonlinear polarization rotation effect, which is of great significance in both basic research and industrial applications.

[0053] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0054] In the embodiments provided in this application, it should be understood that the disclosed methods can be implemented in other ways without exceeding the spirit and scope of this application. The current embodiment is only an illustrative example and should not be used as a limitation. The specific content given should not limit the purpose of this application. For example, some features can be ignored or not executed.

[0055] The technical means disclosed in the present application are not limited to the technical means disclosed in the above-mentioned implementation methods, but also include technical solutions composed of any combination of the above technical features. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of this application, and these improvements and modifications are also regarded as the protection scope of this application.

[0056] The above is a detailed introduction to an all-optical modulator based on a 1.7-micron high-energy all-fiber ultrafast laser provided in an embodiment of the present application. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method and its core idea of ​​the present application; at the same time, for ordinary technicians in this field, according to the idea of ​​the present application, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as a limitation on the present application. Although the present application has been described in detail with reference to the aforementioned embodiments, ordinary technicians in this field should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some of the technical features therein with equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. An all-fiber ultrafast laser based on 1.7 micron high energy, characterized in that: The all-fiber ultrafast laser comprises: a pump source (1), a wavelength division multiplexer (2), a gain fiber (3), a bandpass filter (4), an output coupler (5), a single-mode fiber (6), a first three-ring polarization controller (7), a polarization-dependent isolator (8), and a second three-ring polarization controller (9); The optical fiber output end of the pump source (1) is connected to the input end of the wavelength division multiplexer (2), the output end of the wavelength division multiplexer (2) is connected to the input end of the bandpass filter (4) through the gain optical fiber (3), the output end of the bandpass filter (4) is connected to the input end of the output coupler (5), the first output port of the output coupler (5) is connected to the input end of the first three-ring polarization controller (7) through the single-mode optical fiber (6), the second output port of the output coupler (5) serves as the output of the all-fiber ultrafast laser, the output end of the first three-ring polarization controller (7) is connected to the input end of the polarization-dependent isolator (8), the output end of the polarization-dependent isolator (8) is connected to the input end of the second three-ring polarization controller (9), and the output end of the second three-ring polarization controller (9) is connected to the input end of the wavelength division multiplexer (2); The wavelength division multiplexer (2), the gain optical fiber (3), the bandpass filter (4), the output coupler (5), the single-mode optical fiber (6), the first three-ring polarization controller (7), the polarization-dependent isolator (8), and the second three-ring polarization controller (9) constitute a ring cavity; The first three-ring polarization controller (7), the polarization-dependent isolator (8) and the second three-ring polarization controller (9) form a nonlinear polarization rotation structure, which can be used as an equivalent saturable absorber to achieve mode locking. The saturable absorption effect generated by the nonlinear polarization rotation structure can achieve self-amplitude modulation.

2. The 1.7 micron high energy all-fiber ultrafast laser according to claim 1, characterized in that: The output coupler (5) is connected to the single-mode optical fiber (6) by optical fiber fusion splicing, and when the optical fiber fusion splicing is performed, the loss is controlled within 0.05 dB.

3. The 1.7 micron high energy all-fiber ultrafast laser according to claim 1, characterized in that: The pump source (1) is a fiber laser with a central wavelength of 1570 nanometers. The output end of the pump source (1) is a fiber output with a maximum power of 2 watts.

4. The 1.7 micron high energy all-fiber ultrafast laser according to claim 1, characterized in that: The wavelength division multiplexer (2) is a 1570 nanometer or 1750 nanometer optical fiber wavelength division multiplexer (2), and the pump light emitted by the pump source (1) is coupled through the wavelength division multiplexer (2) and injected into the gain optical fiber (3).

5. The 1.7 micron high energy all-fiber ultrafast laser according to claim 1, characterized in that: The gain optical fiber (3) is a thulium-doped optical fiber.

6. The 1.7 micron high energy all-fiber ultrafast laser according to claim 1, characterized in that: The bandpass filter (4) is an all-fiber bandpass filter, and the overall structure consists of an input optical fiber, a collimating lens, a filter, a focusing lens, and an output optical fiber.

7. The 1.7 micron high energy all-fiber ultrafast laser according to claim 1, characterized in that: The bandpass filter (4) is an all-fiber bandpass filter with a passband wavelength range of 1700±49 nm and an insertion loss of 1.3 dB.

8. The 1.7 micron high energy all-fiber ultrafast laser according to claim 1, characterized in that: The polarization-dependent isolator (8) is an optical fiber polarization-dependent isolator, and its isolation is 34 dB and its insertion loss is 0.88 dB.

9. The 1.7 micron high energy all-fiber ultrafast laser according to claim 1, characterized in that: The single-mode optical fiber (6) is a SMF-28e single-mode optical fiber.

10. The 1.7 micron high energy all-fiber ultrafast laser according to claim 1, characterized in that: The coupling ratio between the first output port and the second output port of the output optical fiber coupler is 80:20.

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